His claim defies a report by the International Atomic Energy Agency last week, which said Iran was slowing down its uranium enrichment programme, increasing the number of centrifuges by only 164 since November.
The announcement of the test run followed Russian officials earlier saying that the plant's construction was complete.
The move is Iran's latest defiance of the UN's demands that Tehran suspend its enrichment programme because of fears it could be used to produce nuclear weapons.
Iran has maintained that it only seeks to create nuclear energy for peaceful purposes.
The Bushehr power plant was built with Russian help and will run on enriched uranium imported from Moscow.
This has worried the West because the spent fuel could be turned into plutonium, a potential material for nuclear warheads.
Alireza Ronaghi, Al Jazeera's correspondent in Iran, said there is still some way to go before Iran has a fully functioning nuclear reactor.
"It's just a step towards the final implementation which is still very long away. It doesn't mean that they are only a few buttons away," Ronaghi said.
"They have told us that they need at least 50,000 centrifuges at Natanz and they only have 6,000," he said.
Aghazadeh said: "We are doing what we need to do in Natanz on the basis of a specific time schedule."
He said tests on the Bushehr plant should take between four and seven months.
"And if they go smoothly, then it [the launch of the plant] will be even sooner," he said.
Yigal Palmor, Israel's foreign ministry spokesman, said the test run was "bad news".
"Iranians are showing again that they are making progress in their nuclear race."
"This should be understood as very bad news for the whole of the international community," he said, and called for, "immediate and very determined steps in order to prevent Iran from becoming a nuclear power."