The man, who is originally from county Laois, produced a knife and demanded cash at the Glencar filling station at around 10 o'clock. Gardai were allerted to the robbery in progress and arrested the man at the scene.
No one was injured in the incident.
The man was charged with robbery at Letterkenny Garda Station and released on bail. He will appear before Letterkenny District Court on the 22nd of April.