In Oklahoma no person may be employed or operate as an armed security guard until a license therefor has been issued by CLEET.
See: 59 OK Stat §59-1750.4a

$141 License fee, consisting of $100 application fee and $41 fingerprinting fee
$50 Upgrade from Unarmed to Armed License

License expires three years after being issued. Cost for renewal is $100

The Council on Law Enforcement Education & Training published an application checklist

According to Oklahoma Statutes (OS) § 59-1750.5(H)(2):

Applicant must be at least 21 years of age

According to OS § 59-1750.5(H)(1):

Applicant must be a citizen of the United States or an alien legally residing in the United States

Not Required

According to Oklahoma Administrative Code (OAC) § 390:27-1-4:

(a)   A certified peace officer will be exempt from firearms requalification for the remainder of the calendar year in which he or she was certified.
(b)   A certified peace officer must successfully complete firearms requalification during the next calendar year after he or she receives peace officer certification.
(c)   Any peace officer changing employment between law enforcement agencies shall not be exempt from annual requalification requirements and must show proof of successfully requalifying during the calendar year while employed as a peace officer.
(d)   One (1) day employed/commissioned/appointed as a peace officer with a law enforcement agency during the calendar year constitutes employment as a peace officer.

Not Required

According to OAC §390:35-5-9
(a)   An identification card shall be issued to all licensees. This card shall clearly indicate that the licensee is authorized by the State of Oklahoma to conduct business as a security guard, armed security guard, or private investigator, or armed private investigator.

(d)   The licensee shall carry his identification card on his person at all times while acting within the course and scope of his employment as a security guard or private investigator.

According to OS § 59-1750.5(H)(4):

Applicant must be of good moral character

According to Oklahoma Administrative Code (OAC) § 390:35-7-8(e):
Two sets of fingerprints must be submitted with the application. The applicant must provide CLEET and the Oklahoma State Bureau of Investigation with individual fingerprints for a state and national criminal history records search.

According to OS § 59-1750.5(H)(7):

The applicant must make a statement regarding any history of illegal drug use or alcohol abuse

According to OAC § 390:35-15-6(a):

While in firearms training, students shall be administered a Minnesota Multi-Phasic Personality Inventory (MMPI), or a CLEET approved equivalent psychological examination, by a person qualified to administer such examinations. The school coordinator shall arrange for the examinations to be evaluated by a licensed psychologist of each student’s choice and at each student’s expense. The results of the psychological evaluations shall be forwarded to CLEET by the evaluating psychologist on forms to be provided by CLEET.

However, according to OAC § 390:35-5-5(b)(4):

Active, full-time peace officers are exempt from the psychological evaluation that is required for armed security guard applicants. Retired, full-time peace officers are exempt from the psychological evaluation for a period of one (1) year from the date of their retirement. This exemption shall apply to any person who possesses CLEET peace officer certification, except when such person has been terminated from a law enforcement agency for failure to exercise appropriate judgment, restraint, and self-control in the use of force, or when there exists clear and convincing evidence of such.

See:
CLEET RULES Sections 390:35-15-6 and 390:35-5-5

See: Application Guide

According to OS § 59-1750.5(H)(6):

The applicant must not have a record of a felony conviction; not have a record of conviction for larceny, theft, false pretense, fraud, embezzlement, false personation of an officer, any offense involving moral turpitude, any offense involving a minor as a victim, any nonconsensual sex offense, any offense involving the possession, use, distribution, or sale of a controlled dangerous substance, any offense involving a firearm, or any other offense as prescribed by the Council, as provided herein.

The Oklahoma State Bureau of Investigation and the Federal Bureau of Investigation conduct background examinations for security guard applicants. Applicants may also have to provide criminal clearances from local police or sheriff departments verifying their criminal histories.
In addition, the CLEET lists disqualifying criminal offenses at Application for Appendix A (page 4)

Not Required