Multiple fire departments responded to a fire at Harp and Hound on Main Street in Islip at about 7:35 a.m. Wednesday morning.
One person was inside the business at the time, but no injuries were reported, according to the Suffolk County Police Department.
The SCPD's Arson Squad is investigating the incident, but police say the cause appears to be non-criminal in nature.
The Islip Fire Department said five other agencies helped it battle the blaze at the restaurant, which is at 528 Main St.