The Seismological center of Bushehr province affiliated to the Geophysics Institute of Tehran University registered the quake at 07:59 hours local time (0329 GMT).
The epicenter of the quake was located in an area 51.8 degrees in longitude and 28.1 degrees in latitude.
Iran sits astride several major faults in the earth's crust, and is prone to frequent earthquakes, many of which have been devastating.
The worst in recent times hit Bam in southeastern Kerman province in December 2003, killing 31,000 people - about a quarter of its population - and destroying the city's ancient mud-built citadel.
The deadliest quake in the country was in June 1990 and measured 7.7 on the Richter scale. About 37,000 people were killed and more than 100,000 injured in the northwestern provinces of Gilan and Zanjan. It devastated 27 towns and about 1,870 villages.