TSA agents found a loaded handgun, which the 79-year-old legally owned, inside Russell's carry-on bag before he was due to fly to Boston.
"Before boarding my flight from Seattle to Boston, I had accidentally left a legal firearm in my bag. I apologize and truly regret the mistake," Russell said in a statement.
"I was issued a citation by the TSA, whose agents couldn't have been more thorough and professional when dealing with this. I really appreciate their efforts to keep air travel safe."
Russell was named MVP of the NBA five times as a player.