The 24-year-old Keller is in his third season with Kansas City after joining the organization as a Rule 5 selection in December 2017.
"Of course I was devastated when I heard the news ... that I had two positive tests," Keller said in a statement Tuesday. "I was sent home yesterday and was hoping the first test was a false positive, but I got the word today that the second test also came back positive, and I have to go into isolation. I am experiencing minor symptoms that remind me more of an allergy attack. Other than that, I feel great and have no other symptoms."
The 26-year-old O'Hearn said he was shocked that his test was positive because he's asymptomatic and feels fine physically. He's also in quarantine.
O'Hearn played in 105 games and hit 14 home runs for the Royals last year in his second stint with the big league club.