Keo resigned with the Broncos on Tuesday, Mike Klis of 9News.com reports.
Keo rejoins the team just a few days after they parted ways. The safety was suspended for the first two weeks of the season but is now able to take the field again. He'll compete with rookies Justin Simmons and Will Parks for a backup safety position.
Charles (knee) remained limited at Thursday's practice.
We'll revisit Charles' status Friday, once the Chiefs' final Week 4 injury report is out, but even if he does suit up Sunday night against the Steelers, it's difficult to imagine the Chiefs handing Charles a heavy workload in his first game back since suffering a torn ACL last October.