"I received the ambassador of Iran, and he invited Brazil to become part of OPEC. It wasn't a suggestion but a formal invitation," he told a media conference.
But Lobao said he told ambassador Moshen Shaterzadeh in the meeting two weeks ago that Brazil "does not envisage that possibility" right now.
Brazil in November 2007 announced it had discovered a new oil field 250 kilometers (155 miles) off its coast that could contain up to eight billion barrels of oil.
Early this year, it said other nearby fields could contain another 40 billion barrels of light crude.
If confirmed by tests underway, those finds would multiply the country's proven national oil reserves, which currently stand at 14 billion barrels, and propel Brazil to the same level as OPEC members Nigeria or even Venezuela.
However the technical challenges in getting to the oil, which lies seven kilometers underwater and under a problematic salt layer, mean production is years away, in 2012 at the earliest.
The cartel of the Organization of Petroleum Exporting Countries (OPEC) is made up of 13 countries, including Saudi Arabia and Iran, which have the biggest reserves in the world.
Lobao said he had not spoken of Iran's offer to other Brazilian ministers and stressed that "there is no discussion underway" on the subject of joining OPEC in the government.
He said that last May, at Saudi Arabia's invitation, he attended an emergency OPEC meeting at which he outlined the perspectives for Brazil's oil industry.
