Some type of "device" came flying through the front window of the Seafood Factory and Bar at 52nd and Market Street in West Philadelphia early Monday morning, police said.
A group of people were inside the restaurant at the time. No one was injured. A small fire broke out but there was no real damage to the restaurant, police said.
The "device" is described as some type of Molotov cocktail with gasoline inside a glass bottle and a cloth wick.
Detectives are reviewing surveillance video as part of the investigation.