Investigators say at 8:40 a.m. Monday, a man walked into the First Trust bank on the 1900 block of Walnut Street and gave a demand note to a teller.
The suspect fled with approximately $2,000 into Rittenhouse Square.
The suspect is described as a black male in his 40's, 5'8" to 5'10" tall, medium build, dark complexion, with a thin mustache, wearing a tight black knit cap and a large tan or yellow parka with a fur-lined hood.
The FBI says the suspect is considered armed and dangerous, and anyone with information is asked to call the FBI at 215-418-4000 or the Philadelphia Police Department.
There may be a reward for information leading to the identification and apprehension of the suspect.