One case was reported at Hillside Intermediate and two others at Bridgewater-Raritan High School, Interim Bridgewater-Raritan Superintendent Thomas Ficarra said.
It was unclear if the individuals were students or teachers.
Those required to quarantine has been contacted.
"It is important to note the district is in direct contact with the local health department officials on every incident related to COVID-19, and is coordinating closely with public health officials and following CDC, state and local health department guidance in order to assure the health and safety of our community," Ficarra said in a letter.
Click here to follow Daily Voice Somerset and receive free news updates.