Kushner spoke to investigators in November for less than two hours, and the dominant topic was Michael Flynn, according to two people familiar with the meeting who spoke to CNN at the time.
The investigation team has not provided comment about Mueller's interest in Kushner's financial dealings, but CNN's report could indicate a suspicion of violating conflict of interest rules, since Kushner served as President Trump's foreign policy point man during the transition while still being involved in some of his family businesses.
In addition to Russian election meddling and foreign financing, Mueller is looking into possible collusion between Trump's campaign and the Russian government.
Mr Kushner's father founded the real estate developer and lender.
Kushner wore many different hats during the transition, including spearheading outreach on behalf of President Trump to "over 50 contacts with people from over 15 countries", according to a statement.
Kushner Companies was nearing a deal for Anbang to invest in the 666 Fifth Avenue building when Kushner sat down with Xiaohui a week after Trump's election.
Kushner has said that the December 2016 meeting was held to discuss official government business. The skyscraper racked up more than $1.4 billion in debt after the 2008 financial crisis, setting the family company scrambling for investors. A lawyer for Kushner said no questioning is taking place, "Nor would there be any reason to question these regular business transactions".
Also during the transition, Kushner met with Sergey Gorkov, chairman of Russian state-run Vnesheconombank. The bank has said publicly that Gorkov attended the meeting as part of a "roadshow of business meetings" that he was conducting in the U.S. Flynn pleaded guilty shortly after to lying to the Federal Bureau of Investigation about his contacts with Russian Ambassador Sergey Kislyak.
This story was first published on CNN.com, "Exclusive: Mueller's interest in Kushner grows to include foreign financing efforts".