Mr Corbyn was a member of Palestine Live group until around the time he became party leader in 2015.
A spokesman for the Labour leader said: “Jeremy and the Labour Party are implacably opposed to all forms of anti-Semitism and will take whatever necessary action to stamp it out in the party.”
Comments posted on the group include conspiracy theories about the Rothschild family, Israel’s supposed involvement in the 9/11 attacks, and links to material produced by neo-Nazi groups.
One of the most shocking posts included an image of a pig with ‘Israel Lobby’ written on its side, with four politicians suckling from it.
There is, however, no evidence that Mr Corbyn himself posted any anti-semitic comments on the site, and a spokesman for the Labour leader last night stressed that he had no knowledge of any such comments.
The spokesman said: “I don’t think anyone is suggesting anything that Jeremy has written in any Facebook group or anywhere else constitutes anti-Semitic comments.
“There were thousands of members of this group. In social media, all sorts of things are posted which often others participating aren’t even aware of.
“It is repugnant if there are anti-Semitic posts – and I gather there are. If they involve anyone to do with the Labour Party then investigation and disciplinary action will be taken.”
Mr Corbyn is reported to have been added to the group, rather than joining himself, but did on occasion post on the page.
Labour has since confirmed that the party has launched an investigation into up to six other members involved in the group, including Corbyn supporters Clive Lewis and Chris Williamson.
Mr Corbyn’s son and Shadow Chancellor John McDonnell’s chief of staff, Seb, and a member of his team, Jack Bond, are also reported to be members.
MPs Mr Lewis and Mr Williamson have since said they were unaware of any anti-semitic or racists comments being made, and have removed themselves from the group.
The CAA has however accused Mr Corbyn of posting comments including the term ‘Zio’, and have said there is ‘no conceivable justification’ for Mr Corbyn’s involvement in the group.
The CAA has also confirmed that they will be filing an official complaint against Corbyn to Labour.
This latest controversy comes amid an on-going row over anti-semitism within the Labour party, which has led to the suspension of numerous senior party members, including former London mayor Ken Livingstone.
Mr Corbyn was reportedly a member of the Facebook group from at least October 2014 to shortly before his election as Labour leader in September 2015.