The report by the IRNA agency said the pilot stage operation of the power plant will start on Wednesday during a visit by the head of Russia's state Rosatom Atomic Corporation, Sergey Kiriyenko.
The long-awaited 1,000-MW power plant, which was built in the city of Bushehr with the help from Russia under a $1 billion contract, was expected to become operational in fall of 2008.
Some 700 Iranian engineers were trained in Russia to operate the plant.
Tehran also plans to build a 360-megawatt nuclear power plant in Darkhovin, in the southwestern Khuzestan province.
The West, which suspects Tehran of seeking to produce its own nuclear bomb, has been critical of Russia's involvement in building Iran's first nuclear power plant. Russia says it is purely civilian and cannot be used for any weapons program.
The head of Russia's state nuclear company, Sergei Kiriyenko, said this month Russia aimed to start up a nuclear reactor at Bushehr by the end of the year. The plant is located on the Gulf cost in Iran's southwest.
Iran's official IRNA news agency said the plant "is in the final stages of its construction" and the Russian side had boosted the number of staff to "increase the speed of work".
Analysts say Iran could become a central issue in relations between Russian President Dmitry Medvedev and new U.S. President Barack Obama, who has said that the United States was prepared to talk to Tehran.
They say Russia has used Bushehr as a lever in relations with Tehran, which is suspected by the United States and some European countries of seeking to build nuclear weapons.
Iran, the world's fourth-largest crude producer, rejects such allegations and says its nuclear program is aimed at generating electricity so that it can export more oil and gas.
Russia started deliveries of nuclear fuel for the plant in late 2007, a step both Washington and Moscow said removed any need for Iran to have its own uranium enrichment program.
Switching on the Bushehr plant could dismay some in the United States, Israel and Europe who are deeply suspicious of Iran's intentions.
Moscow says the plant poses no proliferation risk as Iran will return all spent fuel rods to Russia.