He immediately hit the field for a 30-pitch bullpen session and had no issues.
Keller was the Royals' starter opening day last year. Danny Duffy will take the ball in next Friday night's opener in Cleveland.
"I'm feeling great now,'' Keller said. "This morning I was cleared about 8:30, so that was probably one of the best phone calls I've had. I felt like I got called up to the big leagues or something. It was nuts.''
Earlier in the day, Royals prospects Nick Dini and Daniel Tillo tested positive for the virus. They are now quarantined.