Roberts, who played just 39 games last season because of concussion-like symptoms, is on a rehab assignment and could rejoin the club at some point in June, though Showalter did not speculate on an exact date.
"He's doing well and got back in the lineup [on Monday] after playing last night," Showalter said.
Roberts has played five games for Double-A Bowie and is hitting .222. Showalter plans to have him go through the entire Minor League chain before returning to the bigs.
"The plans are -- not to get to far ahead -- [for him] to play with [Triple-A] Norfolk for about a week," Showalter said. "We talked about wanting him to really finish up competition-wise in Triple-A. That's just tentative."
Roberts, once known as one of the top second basemen in baseball, has been out so long because of what doctors now know about concussions.
"We're getting better and better at things from where that is concerned," Showalter said. "There is so much unknown about it, still. I feel like we have been very cautious and leaning on the doctors. ... I applaud it. It's something we should have been better at all along.
"When someone used to have a concussion, you would hear they would play [the next day]. That's not right."
Roberts is a .281 career hitter with a .353 on-base percentage over parts of 11 seasons in the Majors.