The baby boy, who is yet to be named, was born Saturday morning at a Los Angeles hospital. He was 21½ inches long and weighed 7 pounds, said Elliot Mintz, a spokesman for the star of TV's "Miami Vice" and "Nash Bridges."
Johnson described himself as "over the moon times six," Mintz said.
Mother and baby were both doing well. The couple also have a boy, Jasper, and a daughter, Grace.
Johnson has a daughter, Dakota, with actress Melanie Griffith, and a son, Jesse, with actress Patti D'Arbanville.