The US Securities and Exchange Commission is investigating how IBM recognised revenue for certain deals in the US, Britain and Ireland, the company has said.
IBM, the world's largest technology services company, said it learned of the investigation in August and was co-operating with the SEC, but did not disclose what deals were being probed.
An IBM spokesman told Reuters the company had a "rigorous and disciplined process" for its reporting of revenue.
News of the SEC probe came a week after the company posted lacklustre quarterly results and cut its 2015 profit forecast.
IBM has been a subject of several SEC probes in the past, including a 2013 investigation on how it reported revenue from its cloud computing business. Regulators ended that probe without recommending any action.
Earlier this month, the SEC called financial reporting "a key enforcement priority" as it announced a series of enforcement actions for violations of federal securities laws.
Revenue recognition is how a company records revenue on its books, with discrepancies often arising depending on whether cash is received, or payments deferred. Accounting rules differ in the US and in Britain and Ireland.
A May 2014 change in the accounting standard for revenue recognition has increased scrutiny by regulators.
Separately, IBM also authorised a $4 billion share buyback last night, in addition to $2.4 billion remaining from a previous share repurchase programme announced last October.
Shares of the IBM have dropped steadily in recent months, falling 21% since hitting a year high of $173.97 in April.
Last week, IBM posted a bigger than expected drop in third-quarter revenue and cut its full-year profit forecast as a stronger US dollar accentuated weakness in demand from China and emerging markets.
IBM opened its first Irish operations in 1956 and now has an Irish workforce of over 3,000 in Dublin, Cork and Galway.