The head of Berkshire Hathaway is among a group that includes Dan Gilbert, the billionaire founder of Quicken Loans.
US news reports and the Financial Times said Mr Buffett co-signed a letter from the group and pledged money for a bid.
Verizon, private equity firms, and the owner of the Daily Mail have expressed an interest in Yahoo's assets.
Last month the search company, hit by falling advertising and weakening investor confidence, shortlisted about 10 potential buyers.
News of Mr Buffett's interest could improve Yahoo's sale hopes. He admitted at Berkshire's annual meeting last month that his investment firm had been slow to get involved the new tech industry.
Mr Buffett, whose firm has a stake in IBM, said in an interview on 2 May that Yahoo's business had deteriorated significantly and that "something has to change there". But he did not mention any potential bid.
Reuters, which first reported Mr Buffett's involvement, pointed out that Susan Decker, who worked at Yahoo in several senior roles between 2000 and 2009, is now a director on Berkshire's board.
The news agency quoted an interview she gave to CNBC television on 29 April: "I hope the next owner can do something to revitalise the spirit of the core things that made Yahoo very, very unique and create a distinction in consumers' minds about why they love Yahoo still.
"It will be helpful if it is private or part of a much larger corporation to achieve that," she said.
However, Verizon is thought to remain the frontrunner in the bidding for Yahoo.
The US telecoms giant would merge Yahoo with AOL, which it bought for $4.4bn (Â£3bn) last year to create a digital group capable of taking on the likes of Google and Facebook.
Legendary investor Warren Buffett is backing a consortium bidding for Yahoo's core internet assets, according to reports.