The Portuguese has been appointed as Louis van Gaal's successor, on a three-year contract worth £45m, with the option of an additional year.
Although he is not a fan of Mourinho, Keane admits that the former Chelsea boss will bring back United's winning mentality.
"He is not my cup of tea. I found him really irritating when I coached against him, but that is just a personal thing," he told ITV.
"Working at Manchester United is all about winning and his CV will tell you he is a winner.
"He was always going to be a good option when United didn't qualify for the Champions League.
"He was available, fantastic CV and it seems like a good fit, but maybe he is not for me."
