State television described the incident in a volatile region near the Pakistani border as a "terrorist attack."
It said a suspect tried to enter the Imam Hossein mosque in Chabahar port as people gathered for Friday prayers, but was stopped by security guards.
As he started to run away, he set off his explosives, killing two passers-by and wounding several people, including policemen. It was unclear if the explosives were detonated by accident.
No group claimed responsibility for the attack but the Sunni militant Jundallah group, which claims to be fighting for Sunni rights in the mainly Shiite Iran, has been involved in sporadic bombings in the region in the past.
In an obvious reference to Jundallah, lawmaker Yaqoub Jedgal blamed the explosion on "remnants of terrorist groups," according to the semi-official ISNA news agency. Jedgal is a representative from Chabahar in the Iranian parliament.
Jandalla's insurgency in the southeast suffered a significant setback in 2010, when Iranian authorities arrested and later executed the group's leader, Abdulmalik Rigi.