Police said the incident occurred just before 9 p.m.
Police said the robber, believed to be in his 20s or early 30s, entered the store, "simulated a weapon" and demanded the clerk hand over cash.
The store employee, identified by police as being a 35-year-old man, complied -- and handed the robber cash from the register. It was not immediately clear how much was taken.
Police said the robber then fled the store onto southbound Harrison Avenue. No one was injured in the robbery.
Police are asking anyone with information the incident to call Crime Stoppers at 800-244-TIPS. All calls will remain confidential, police said.