"Art had an issue," Harbaugh said. "It's not football-related. I'm going to leave it to Art to explain what it was. It's more of a personal health thing that's not serious. We just held him back this week."
Jones has been sidelined since the Ravens resumed practice Sunday following a 34-27 loss to the Carolina Panthers on Thursday night.
Jones was at team headquarters today.
Harbaugh said backup quarterback Tyrod Taylor is improving after being evaluated for concussion symptoms and has passed a physical balance test. He's expected to miss the Ravens' preseason finale Thursday night against the St. Louis Rams, but Harbaugh didn't officially rule him out.
The Ravens could go with third quarterback Caleb Hanie and recently signed fourth quarterback Dayne Crist exclusively against the Rams.