Kellenberg Memorial High School, at 1400 Glenn Curtiss Blvd., in Uniondale was alerted to the call just after 7 a.m., Nassau County authorities said.
The call was made anonymously to the 988 Lifeline, a suicide and crisis hotline. The caller claimed to have planted bombs around the school grounds.
Police and Homeland Security agents had teachers and students wait outside until they deemed the area safe.
Officers are investigating who made the call.
Click here to follow Daily Voice Bethpage and receive free news updates.