It happened around 2:00 Friday afternoon at the Beneficial Bank branch on the 1400 block of Rhawn Street.
Authorities say the suspect walked in, brandished a gun and demanded money from the teller.
After getting an undisclosed amount of cash, the suspect fled, possibly in a black SUV.
Police say the suspect is described as a black male, 6'' tall, 240 pounds with a medium complexion.
He was last seen wearing blue jeans, black shoes, black gloves, a red baseball cap with an unknown white logo, and a gray hooded sweatshirt.
Authorities consider him armed and dangerous. Anyone with information about the robbery or the suspect is urged to call the FBI at 215-418-4000 or Philadelphia Police at 215.686.TIPS (8477).
Police say there may be a reward for information leading to the capture and tipsters can remain anonymous.