The official Islamic Republic News Agency said Mohammad Reza Aghazadeh had been handling cases involving large land transactions near Karaj, an industrial satellite city to the west of Tehran.
"He is now in surgery," Justice Minister Jamal Karimirad said on Sunday. "I hope God helps us keep him alive."
An official close to the case said the judiciary was forming a committee to discuss a rash of attacks against judges in the last four weeks.
A judge was stabbed to death in the southern province of Fars earlier this month, and another was disfigured when acid was thrown on his face in the southwestern province of Khuzestan, the official said.
Hassan Moghaddas, a judge who sentenced several reformist dissidents to jail, was shot and killed in his car on 2 August.