One man, who was shot in the head, died at the hospital Wednesday morning. Another man was punched in the face and is in stable condition.
Customers were held inside the restaurant as deputies searched the area.
"I heard two gunshots and then maybe five minutes later these two guys came into BJ's, looked around, spread out and we never saw them again. The cops came in, they were there real quick as you see and they just run," said Jonathan Vazquez, a witness.
Sheriff's investigators say it's not known whether the attack was gang-related. They have made no arrests.
Anyone with information is asked to call L.A. County sheriff's homicide detectives at (323) 890-5500.