A student at Pennwood Middle School in the Pennsbury School District is showing symptoms.
The school sent a letter to parents on Saturday.
The health department is waiting for the final test results.
Temple University held two vaccine clinics last week, as the school deals with more than 100 cases of the mumps.
Over 4,800 vaccinated against mumps during Temple clinics
Mumps is spread through saliva and respiratory secretions.
It can take anywhere from 16 to 18 days to develop symptoms after exposure.