The head of Berkshire Hathaway, also known as the Sage of Omaha, is reportedly among a group that includes Dan Gilbert, the billionaire founder of Quicken Loans.
US news reports and the Financial Times said 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 all expressed an interest in Yahoo's assets.
Buffett will face stiff competition. Last month the search company, which has suffered falling advertising and weakening investor confidence, shortlisted about 10 potential buyers. Verizon is tipped as the favourite to win Yahoo's hand.
News of Buffett's interest could improve hopes that Yahoo will clinch a sale. It could also fill a gap in Berkshire Hathaway's portfolio. He admitted at the firm's annual meeting last month that it had been slow to get involved the new tech industry due to what he viewed as its sky high valuations.
Reuters, which first reported Mr Buffett's alleged 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.
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.
Yahoo is being buoyed by its stake in Alibaba, the Chinese e-commerce giant. The holding is worth tens of billions of dollars.
Full story: Warren Buffett eyes Yahoo: City A.M.