Both men were Antioch residents, a deputy coroner said.
Antioch police found the victims in a bedroom of a house at 2809 Carmona Way around 7:45 p.m. They were both pronounced dead at the scene.
Several other people were in the home at the time of the shooting but were not injured, police said.
The first shooter was described as a Hispanic man in his 20s with short hair. He was wearing a long black hooded sweatshirt and khaki pants.
The second shooter was described only as a black man in his 20s wearing a black hooded sweatshirt.
Anyone with information about the case is asked to call Antioch police Detective Diane Freier at (925) 779-6938