Iran state television said the tremor struck just after 7am (0331 GMT) on Sunday and was centred close to the town of Saravan, close to Iran's borders with Pakistan and Afghanistan.
No casualties were immediately reported, although the television said some houses were partly damaged, with windows broken. The town lies 1350km southeast of the capital, Tehran.
"The windows of some homes were smashed and some walls were damaged," said Interior Ministry spokesman Jahanbakhsh Khanjani.
"As it was in a sparsely populated area we are not expecting many deaths or casualties," he added.
Iranian authorities said rescue teams were dispatched to the area to evaluate the situation and to search for victims.
Sunday's earthquake is the second to hit Iran in less than a month after a powerful tremor with a magnitude of 6.4 struck the neighbouring Kerman province on 22 February, killing more than 600 people and destroying several villages.