The source, speaking under condition of anonymity due to restrictions on speaking to the media, said terrorists attacked the Nusaybin Religious Vocational Secondary School in Mardin province. The source did not provide any information on the extent of the damage to the building.
Nusaybin, situated by the Syrian border, has been the site of a recent counter-terrorism operation.
Firefighters attending the scene were attacked by PKK members and unable to put out the blaze.
Tuesday also saw an arson attack on the Misak-i Milli Secondary School in Nusaybin district that caused substantial damage.
The PKK - listed as a terrorist organization by Turkey, the U.S. and EU - resumed its 30-year armed campaign last July. Since then, more than 260 members of the security forces have been martyred and thousands of PKK terrorists killed, according to officials.