The Dragon One restaurant is located in a plaza off Miamisburg-Centerville Rd.
The customer called 911 and said, "We've just been robbed. Dragon One Restaurant on 725. Next to Odd Lots."
The man made the call after he walked in on the robbery in progress.
"I came to pick up my food and they were being robbed when I got there," said the caller. "They had me hunkered down in the back."
Authorities said two of the thieves were armed. One was pointing a handgun and the other held a stun gun.
Witnesses said the men were Hispanic.
One of them came back to the restaurant when an employee tried to watch their getaway plan.
The 911 caller said, "The lady at the restaurant, she tried to come out and see where they were going. The guy with the gun actually came back and tried to slam the door on her, pointing the gun in her face."
All three men had short, black hair and were wearing baseball hats. Two of the men appeared to be in their 30s or 40s, and the third man may have been a young adult or teenager.
Police said the three got away with an undisclosed amount of cash. No one was hurt.
Anyone with information about the crime should contact the Montgomery County Sheriff's Office. .