The robbery happened around 3:52 p.m. Friday at the Citizens Bank at 7327 Frankford Avenue.
Police say the suspect handed a teller a threatening demand note and obtained an undisclosed amount of cash.
The suspect then fled on foot east on Teesdale Street.
He is described as a black male of about 20 years of age with a thin build standing 6'1" tall. He has a mustache and a goatee wearing a red Phillies hoodie, an Eagles hat, sunglasses, black mask, blue jeans and dark-colored shoes.
Anyone with information can contact the Philadelphia Police Department at 215-686-TIPS or through phillypolice.com.