The sanctions would ban the remittances of money to Iran from Japan, the Yomiuri newspaper said, citing unidentified sources.
Japan has tried to seek a diplomatic solution to the standoff over Iran's nuclear ambitions, but with Iran still uncommitted to a package of incentives offered by other nations, the Japanese government is considering stronger measures, the report said.
Chief Cabinet Secretary Shinzo Abe, when asked about Iran on a Sunday morning talk show, declined to say whether Japan was considering sanctions and said the government is still pushing for a diplomatic resolution.
But he said he doubted whether sanctions would be effective against Iran, given the windfall profits the country is making on the currently high price of oil.
"It might not damage Iran, but could cause confusion in the world economy," Abe said on TV Asahi's Sunday Project.
On Thursday, Foreign Ministry Taro Aso urged Iran to accept a U.S. offer for direct talks in return for suspending its controversial uranium program, but said Tokyo was not considering economic sanctions.
Foreign Ministry officials were not immediately available for comment Sunday afternoon.
Local news reports have said the United States is urging Japan to consider restricting financial transactions with Iran should diplomatic efforts fail to break the diplomatic impasse. Some have said Washington is pressuring Japan to freeze plans to develop oil fields in Iran, although both sides have denied the reports.
Japan, a top U.S. ally that also imports much of its oil from Iran, has been keen to play a mediating role in resolving the standoff.
Japan has started to curb crude oil imports from Iran amid the nuclear controversy. Oil shipments from Iran fell by 20 percent in April compared to a year earlier, according to Trade Ministry data.