Ten other Afghans suffered injuries in the accident, which occurred between Tehran and the central city of Qom, about 125 kilometres (77 miles) southwest of the capital, the television report said.
The accident happened early in the evening.
It comes as authorities in Iran report an influx of Afghans fleeing insecurity in their country, which borders the Islamic republic.
The governor of Sistan-Baluchistan province, which borders Afghanistan and Pakistan, warned that Iran needed to prepare for a tide of would-be migrants.
"All regions of the country must prepare for the arrival of a wave of Afghan migrants... Who come with all their families and are in a dire situation," he said.
"We must take further steps" to deal with the influx, he said.