It happened at about 10:30 Sunday night at 13th and R Streets.
The store was open at the time but no customers were inside.
One employee told police a suspect wearing a dark blue hooded sweatshirt, gloves, and a scarf over his face entered McDonald's carrying a black semi-automatic handgun.
The suspect reportedly told the restaurant manager he had 25 seconds to go to the safe and fill a bag with cash and then began to count backwards from 25.
The gunman is at large.
There is no word on how much cash was stolen.
No one was hurt.