The couple had a quiet wedding at the Beverly Hills courthouse's ceremony room, said Alba's representative, Brad Cafarelli.
The couple were casually dressed -- Alba wore a long blue dress and tied her hair back in a ponytail while Warren was in a white shirt and brown trousers.
People magazine, quoting a source, reported that the couple applied for a marriage license on Monday and waited about 40 minutes for the paperwork to be processed before a staff member from the courthouse married them.
According to the source, nobody else attended the wedding.
The couple, who met while filming for Fantastic Four, are expecting a daughter this summer.
Photograph: Getty Images