A report of a potentially armed person inside Burlington City High School temporarily placed the school into a lockdown.
The incident happened Tuesday around 12:50 p.m.
School officials told police they thought someone in the building had a gun.
Police found no threat at the school, and the area was deemed safe.
As a precaution, classes and all after school activities were canceled.
There have been no arrests, and no firearm was recovered during the search.