They also activated nose tackle Casey Hampton, but that's not the headline here. Mendenhall's activation is a surprise because general manager Kevin Colbert said as recently as last week that he expected Mendenhall to start the year on the reserve/PUP list. That would have ruled Mendenhall out for the first six weeks of the season. Mendenhall is no longer eligible for the list.
The running back is expected to be out for much of September, a source told ESPN's Adam Schefter on Friday.
"I've been talking to (Mendenhall), and he's been saying he's been feeling good," backup running back Isaac Redman said, via The Associated Press. "He's been cutting and running at full speed, so it's just a process with him coming in live now and being able to take hits."
The activation on Friday is a sign that the Steelers are hopeful for a speedier recovery. Even if Mendenhall can't get ready for the season opener, they probably wouldn't take this step unless there was hope he could get ready sometime in the season's first month.
The news comes at just the right time for Pittsburgh. They are quite thin in the backfield with Redman also struggling with injuries.