He added: “That’s no excuse. Karl Marx was a Jew, at least a Jew by heritage. So that’s no excuse.”
Mr Sanders did not endorse Mr Corbyn in the 2019 general election, and has not publicly backed him since doing so in 2017.
He will contest the Iowa caucus this week – the first of 50 primary elections in the race for his party’s nomination for president.
An early frontrunner, Mr Sanders is hoping to become the first Jewish president of the United States.
Prof Dershowitz, a renowned expert on criminal and US constitutional law, has received negative media attention in recent years for his previous association with Jeffrey Epstein.