Surveillance video of the crime was released on Saturday.
Detectives say a man walked into the restaurant at 3401 Street Road just after 5:30 p.m. on Friday.
He ordered a cup of coffee and was in the process of paying for it when he jumped over the counter and cleared out the cash register.
The clerk wasn't hurt.
The bandit fled in a late model Jeep Cherokee that was blue or green in color.
Police say the suspect was spotted in the same store the day before the robbery.
If you recognize the man, you are urged to call Bensalem Police at (215) 633-3668 or call the anonymous tip line at (215) 633-3660.