It happened around 5:30 p.m. Thursday at the grocery store located on the 6600 block of Roosevelt Boulevard.
Police say the suspect stole about $4,000 and then fled the scene.
No injuries were reported in the incident.
Northeast Detectives believe the suspect may have been involved in several other robberies, including one at a nearby Boston Market last week.
A description of the suspect has not been released.
Anyone with any information is asked to call police at 215-686-TIPS.