Somehow the man sneaked into the passport control area of Terminal 1C around 3 pm on Wednesday, pulled out his gun and threatened four officers, police said.
The officers managed to overpower than man and he was arrested. A gas pistol is a non-lethal weapon that fires a gas cartridge, producing a blast that can cause injury at a range of up to four metres but does not shoot an actual projectile. Officials did not release his name, but said the man is mentally ill and is 29-years-old.
Authorities were unable to immediately explain how the man got into the passport control area.
A police spokesman would not confirm reports that the suspect had a combat knife in his pocket. It has been confirmed, however, that he had a machete in his car.
He is now under investigation for possible violations of weapons, drugs and aviation security regulations.
The scare is the latest blatant security failure at Frankfurt Airport.
Last weekend, officials confirmed that 10,000 workers had not undergone necessary routine security checks.
And in March this year, an Islamist terrorist killed two US airmen outside the airport as they boarded a bus used to transport troops American military facilities.