Elizabethton Fire Chief Barry Carrier said there was no fire.
Fire Marshal Jack Buckles was on the scene and trying to determine why the fire suppressant system activated. Buckles will announce his findings later on Friday.
The incident caused excitement as fire department vehicles hurried to the restaurant just as the noontime rush was getting started. The fire trucks were on the scene for only a short time before returning to station.
Fire suppressant systems are required for commercial restaurants in order to quickly extinguish fires that break out in the cooking areas.
The restaurant was back open in less than an hour.