It happened around 3:51 p.m. at the Beneficial Bank located at 826 East Allegheny Avenue.
Police say the suspect presented a demand note to one of the tellers.
After receiving an undetermined amount of cash, the woman fled the scene on foot.
She is described as a Hispanic woman about 5'6 to 5'8 tall with a ponytail. She was wearing a white T-shirt, black Capri pants, sandals, earrings and a bracelet or band on her right wrist.
She may have dye stains on her skin and clothing.
No injuries were reported.
Police say the suspect is considered armed and dangerous.
Anyone with information about this suspect is asked to call the FBI at 215-418-4000 or the Philadelphia Police Department. There may be a reward for information leading to this subject's capture, and tipsters can remain anonymous.