The 29-year-old joined the U's on a free in May 2015 but has made only six appearances for the League Two side.
He spent part of last season on loan at Stevenage and has also spent time with Luton and Preston.
"I'm very excited to be here. I've worked hard throughout pre-season and I'm desperate to get back playing football," Keane told the club website.
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League One Rochdale have signed midfielder Keith Keane on loan from Cambridge United until January.