It happened at the Sovereign Bank branch at 258 High Street in Pottstown around 1:17 p.m. Tuesday.
Investigators say the man came into the bank armed with a handgun, announced a robbery and demanded cash from the teller.
The robber, who was wearing a BMX-style mask, even forced a customer to the ground.
After obtaining an undisclosed amount of the cash, the suspect fled.
The man police are looking for is described as a black male, 6'2" tall, wearing a gray "Air Jordan" hooded sweatshirt with the hood pulled up, dark sweat or athletic pants, white sneakers, and white gloves.
He is considered armed and dangerous.
Anyone with information is asked to call the FBI at 215-418-4000.
