Elmwood Park Memorial High School and Middle School were both placed on lockdown after 10:00 a.m.
Officials said as a precautionary measure all Saddle Brook schools were also placed in lockdown for a brief period of time.
Elmwood Park police had received information regarding a threat made to the high school, officials said in a statement.
The threat was isolated to Elmwood Park Memorial High School.
The high school and the middle school remained locked down until dismissal time.
Police say the students were always safe and keeping the school on lockdown until dismissal was done as a precaution.
No students were injured. No arrests have been made, but it remains under investigation.
No further details were released.