Rivera, now the head coach of the Washington Football Team, announced in August that he had squamous cell carcinoma (SCC) in his lymph nodes.
Rivera caught his cancer early thanks to a self-check.
He's undergone seven weeks of treatments, and doctors said they are pleased with his progress.
Rivera will still have several weeks of follow-ups and scans, but he says his outlook remains good.
"I've been told it's headed in the right direction," Rivera said.
He will continue with his coaching duties as he has all season.