The central-government investigation, which started early this year, focuses on "regulators who greenlighted the initial public offering, local officials who advocated it and big state firms that stood to gain from it", according to the report.
Ma's relationships with these "state stalwarts" are also being examined as part of the investigation, the report said.
The Wall Street Journal previously reported that Ma had offered in a November meeting with regulators to hand over parts of Ant to the Chinese government.
Ant denied that a divestment of Ma's stake was ever under consideration. "Divestment of Mr. Ma's stake in Ant Group has never been the subject of discussions with anyone," an Ant spokesman said in a statement.
Regulators in China have punished e-commerce giant Alibaba with a massive $2.78 billion (18.2 billion yuan) fine over practices deemed to be an abuse of the company's dominant (and monopolistic) market position.
Alibaba in particular has remained under scrutiny since last year, when co-founder Jack Ma criticised Chinese regulators as being "behind the times", after the company's financial arm Ant Group was investigated.
The penalty, equivalent to around 4% of Alibaba’s 2019 revenues, comes amid an unprecedented regulatory crackdown on home-grown technology conglomerates in the past few months that have weighed on company shares.
Last year, Chinese premier Xi Jinping blocked Ant Group's initial public offering, as it was speculated that the decision was based on Jack Ma's public criticism of Jinping's financial oversight campaign, and that it could add risk to the financial system.
A group of well-connected Chinese power players backed the company; including those linked with political families that pose a potential challenge to Jinping's authority.