A group of protesters set fire to a security services office in Port Said early in the early hours of Tuesday morning.
The building belongs to the National Security Apparatus, part of the interior ministry, which was known before the January 25 revolution as State Security Apparatus.
According to an Ahram reporter in Port Said, the angry protesters torched the garage area of the building, destroying at least six cars.
Armed forces units with tanks and armoured vehicles came to secure the building and to disperse the angry protesters by firing shots in the air.
The building was reportedly still open on Tuesday.
Protesters in Port Said have already torched parts of the Port Said security directorate, angry at police brutality in dispersing protests in the city on Monday.
At least 352 were injured in the clashes on Monday between security forces and protesters, according to the ministry of health.