The alleged threat was made around 5 p.m. and prompted the school's police department to advise the public to stay away from the campus, and for students who were already there to stay indoors or leave campus.
The unidentified person was taken into custody about three hours after the online threat was posted on a private social media account. The suspect was not a CSUN student, police said, adding that the individual has a history of making threats towards schools.
"The Department of Police Services deems there is no longer a threat to the campus," a statement released shortly before 8 p.m. Sunday said. "The University is open and operational."
Details about the threat that prompted the arrest, or any previous alleged threats by the suspect, were not disclosed.
City News Service contributed to this report.