Investigators believe Mr Bannon may hold crucial information on the Trump administration, including details on why former FBI Director James Comey was fired by the president.
Mr Comey has previously said he has "no doubt" that he was fired by Mr Trump to "change" the Russia investigation, a charge the White House denies.
It is not clear what Mr Bannon was questioned about, but he is reported to have spent around 20 hours speaking with Mr Mueller's team.
A source close to the process though told the Associated Press that Mr Bannon answered every question put to him.
http://www.bbc.com/news/world-us-canada-43079550
Mr Comey has previously said he has "no doubt" that he was fired by Mr Trump to "change" the Russia investigation, a charge the White House denies.
It is not clear what Mr Bannon was questioned about, but he is reported to have spent around 20 hours speaking with Mr Mueller's team.
A source close to the process though told the Associated Press that Mr Bannon answered every question put to him.
http://www.bbc.com/news/world-us-canada-43079550
