It happened around 9:50 p.m. Saturday at the Possum Park Mall Shopping Plaza on Capitol Trail.
Police say the male suspect went behind the restaurant counter and sprayed an employee with a chemical agent.
The suspect then forced another employee to give him an undisclosed amount of money from the store's safe.
Investigators say those workers suffered minor injuries.
Police are still looking for the thief.
Anyone with information about the case is asked to contact Det. D. Armstrong by calling (302) 365-8440.