Transportation Security Administration spokeswoman Carrie Harmon tells Fox 5 Atlanta the gun was discovered in a carry-on bag around 9 a.m. Sunday during the X-ray screening process.
TSA officials say they notified Atlanta police of the gun, and a small-caliber round was discharged inside the carry-on bag while officers were handling it.
Authorities say the shot was contained to the bag, and no one was injured.
Officials said the passenger who brought the bag into security was taken into custody. Details about the passenger were not released.
Authorities say the gun discharged at the main security checkpoint at Hartsfield-Jackson Atlanta International Airport, the world's busiest airport.