University spokesman Paul Browning said the school's president ordered the evacuation as a precaution at noon.
Los Angeles police spokesman Richard French said the threatening caller said a bomb was on campus but did not detail where. A bomb squad was dispatched, but the search was called off at about 2:30 p.m.
The university east of downtown Los Angeles has about 20,000 students, though most aren't full-time.
Jon Beaupre, a journalism professor at Cal State LA, said the fire alarm went off at 12:15 p.m. in the middle of his lecture and the class followed normal evacuation procedures. When students arrived outside, they were told there was a bomb scare and the entire campus was being evacuated.
"That led to a mad dash, grabbing bags to get people out of here," Beaupre said.
Beaupre spoke by telephone to The Associated Press while driving in his car and trying to maneuver through heavy traffic. He described a half dozen police cars around campus and a sheriff's helicopter circling overhead.
"Apparently we can get people out of the buildings, but getting traffic away from campus is not easy," Beaupre said.
Two high schools also share Cal State LA's campus, and Beaupre said about 60 students could be seen milling around on a street corner after the evacuation.
Beaupre estimated that the evacuation involved about 8,000 students.
Browning said the university would likely not reopen Thursday.