Matthew Lamar McDaniel, 32, of Atlanta was arrested Saturday at Hartsfield-Jackson International Airport, The Atlanta Journal-Constitution reported. He was freed on $5,700 bail.
McDaniel, who was not on duty at the time of his arrest, told investigators he had put the gun in his bag after cleaning out his girlfriend's car and had forgotten about it, a police report said.
Susan Chana Elliott, a Delta spokeswoman, said the airline is conducting its own investigation. In the meantime, McDaniel remains an employee and is not barred from flying, she said.
Chana Elliott said people are frequently caught with loaded firearms during security checks.
"This happens to lots of people," she said. "They forget to take their guns out of their cases."
Some on-duty pilots are allowed, under a federal program, to bring guns with them in secured cases. This would not apply to McDaniel.
The Georgia Legislature has passed a law that would allow licensed owners to carry their guns in the unsecured areas of airports, but Gov. Sonny Perdue has not yet signed it.