Several unidentified individuals set fire to dried leaves and tree branches in the forest, east of Tehran, which were being collected by city officials, the state-run news agency Fars reported.
The blaze quickly spread to cover a vast section of the forest.
Fire-fighters battled the flames for some six hours before the situation was brought under control.
There were no casualties, according to media reports.
A second fire broke out in the forest at 3 a.m. on Saturday which spread rapidly from burning woods that had not been put out entirely.
Emergency teams were battling the blaze until after 7 a.m.
Lavizan-Shian is a military site in northwest Tehran. Inspectors from the International Atomic Energy Agency became interested in the site after the opposition National Council of Resistance of Iran charged in May 2003 that Irans Revolutionary Guards were conducting clandestine nuclear activities there.
Soon after, Iran razed buildings and removed topsoil from the site to eliminate traces of illegal activities there.
In April 2004, the NCRI revealed that Iran had transferred work and equipment from the site to another nearby military site, which later became known as Lavizan II.
