Chefs at the restaurant, located at 1171 Locust St., were cooking some tri-tip at about 2:15 p.m. when there was a flare-up, spokesman Lewis Broschard said.
The flames spread into some ducting that went up into the attic, where more grease caught fire inside the ducts.
The heat from the ducts then ignited some flammable material that had been stored next to them in the attic, Broschard said.
Firefighters had to climb through a hatch inside a janitor's closet to get up into the attic to reach the flames.
They had the fire under control by 3:11 p.m.
"It was just a very stubborn fire," Broschard said.
He said firefighters could see smoke coming out of the top of the building, but at first they had trouble finding its origin.
The building sustained some smoke and water damage, but the restaurant will likely be able to be re-opened soon, Broschard said.