South Orange Police confirmed the threat around 5 p.m. Wednesday.
The threat was made through social media.
Only two buildings had people in them because school is in its summer session.
Public Safety closed the campus and did a full sweep of every building, around 30 of them.
Several hundred people who were on campus for summer session were evacuated. All evening classes were cancelled. There are about 200 students living on campus over the summer.
Seton Hall University released a statement saying: "This afternoon, Seton Hall University was notified by the South Orange Police Department of an online posting of a bomb threat to the main campus. As a precaution, the police department in conjunction with the university's public safety department closed the campus and began a full sweep of all buildings. In addition, all individuals have been evacuated from the buildings on campus and all evening classes have been cancelled. The University takes threats of this nature seriously and is working closely with police officials to investigate the matter."