According to Nicki Jhabvala of the Washington Post, Rivera said: "What I've been told is it's headed in the right direction."
Jhabvala added that Monday is scheduled to be Rivera's final day of treatment, although he will have to undergo additional scans afterward.
In August, Rivera announced that he had been diagnosed with squamous cell carcinoma in his lymph node. Rivera called the cancer "very treatable and curable," and said he intended to continue coaching while undergoing treatment, which he has.
The 58-year-old Rivera is in the midst of his first season as head coach of the Washington Football Team after coaching the Carolina Panthers for the previous nine seasons.
Rivera went 76-63-1 as head coach of the Panthers, led them to the playoffs four times and took them to the Super Bowl in 2015 after going 15-1 in the regular season. Rivera was named NFL Coach of the Year twice in Carolina.
Washington is off to a slow start this season at 1-5, and it has lost five games in a row since upsetting the Philadelphia Eagles in Week 1.
Rivera benched second-year quarterback Dwayne Haskins in favor of Kyle Allen, calling it a "gut feeling" this week. The move nearly paid dividends against the New York Giants last week, but Washington missed a go-ahead two-point conversion and lost the game 20-19.
Despite being just 1-5, Rivera has Washington very much in the NFC East race, as the division-leading Eagles are only 2-4-1 and have already lost to Washington.
Washington will host the NFC East rival Dallas Cowboys in a huge divisional clash Sunday, followed by a bye week and then a second meeting with the Giants in Week 9.