The person is said to have been a member of the country's notorious Basij militia.
"A 21-year-old member of the Basij from the city of Kuhdasht was killed last night by rioters while defending public order," state television reported, citing the deputy governor of Lorestan province, Said Pourali.
Iranians have been protesting against skyrocketing costs and falling living standards in recent days, with clashes with security forces reported from several parts of the country.
