"He is up and moving around, speaking sensibly, working at a laptop," Oestreich said in a statement to The Associated Press.
O'Neill said in an e-mail that Keillor "is doing well and the family appreciates the warm wishes."
In a statement, Keillor said he was "feeling ill" on Monday morning and drove himself to United Hospital in St. Paul, where he lives, then was transferred to Mayo "simply because they know so much more about me down there."
Keillor, 67, underwent surgery to repair a heart valve at the Mayo Clinic in 2001.
"I am in the hands of smart and compassionate people and plan to get out on Friday and get right back to work," including the opening of a new season of "A Prairie Home Companion," Keillor said. "And that's the news from here."
Mayo Clinic initially said Keillor was hospitalized Sunday, but Keillor's publicist said it was Monday. Oestreich later confirmed it was Monday.
Keillor is scheduled to open the new season of "A Prairie Home Companion" on Sept. 26 from the Fitzgerald Theater in St. Paul.
He celebrated "Prairie Home's" 35th anniversary with a Fourth of July performance before some 10,000 people in Avon, a central Minnesota town that helped inspire his fictional hometown of Lake Wobegon. He performed last Friday night at the Minnesota State Fair.
Some 4 million people listen each week to "A Prairie Home Companion" on nearly 600 public radio stations in the U.S.
On the Net:
A Prairie Home Companion: http://www.prairiehome.org