Chess was outlawed in 1981 because it was thought to encourage betting, which is forbidden in Islam. But in 1988 the Islamic republic's founder Ayatollah Ruhollah Khomeini issued a fatwa, or Islamic religious decree, permitting chess as long as no gambling was involved.
The game, driven underground, made a vigorous comeback.
"One day I went to a park near my home to get a notebook from my friend and ... saw two grown-ups playing chess on a bench," Mahjoob told AFP.
Read more in Grandmaster's next move: A chess revival in Iran.