It happened at 4:47 p.m. Monday, at the branch in the 5100 block of Frankford Avenue.
Police say the man walked into the bank, gave the teller a threatening note and fled on foot with an undisclosed amount of cash.
Surveillance cameras captured a picture of the man.
Investigators released the following description:
White male, 30 years old, 5'6", medium build, beard, wearing a green jacket with fur around the hood and a dark colored baseball hat.
Anyone with information on the crime or the suspect is asked to contact the FBI/PPD Violent Crimes Task Force at 215-418-4000.