Princeton University confirmed that there was no armed gunman on the campus on Wednesday morning, following a earlier false alarm.
At 11:25 a.m., Princeton University's Department of Public Safety issued an all clear, the university's website confirmed.
Princeton said all campus activities have returned back to normal.
The alarm began at 10.36 a.m. after a male was spotted, with what appeared to be a handgun, near the vicinity of Dod Hall dormitory.
Public Safety responded immediately by issuing a campus alert instructing people to stay indoors, by patrolling and by limiting access to campus.
There was no report of any threatening behavior or injuries, Princeton said.
However, four juveniles - who are not Princeton University students- were taken into custody after being spotted with a toy gun, New Jersey State Police said on the Web site Twitter. The state police said they had been given the information by Princeton University police.