The PSNI said detectives from the organised crime branch arrested the two men and a woman around 9.30pm last night.
The arrests were made at Britton's Court in the Ballymurphy estate.
Police said the arrests were made during a planned operation. The weapon was taken away for further examination.
The three people were released this afternoon pending further inquiries.
The PSNI say one of the men has since been re-arrested.
He is being questioned in connection with an armed robbery at a bookmaker's shop in west Belfast earlier this month.
