The team may also see modification or loss of draft choices in 2014, the NFL said Wednesday in announcing the disciplinary action.
The Steelers had pulled within 13-7 of Baltimore in the third quarter of a key AFC North game on Thanksgiving when the Ravens' Jacoby Jones took a kickoff down the left sideline.
He appeared to be heading for a touchdown but Tomlin, apparently watching the return on a stadium video screen and with his back to the play, took one step onto the field. This caused Jones to slow and he was tackled from behind.
The Ravens got a field goal out of the possession and ended up winning 22-20.
There was no penalty called by game officials and Tuesday NFL officiating head Dean Blandino said that Tomlin should have been penalized for unsportsmanlike conduct. The league followed with Wednesday's $100,000 fine and threat of draft sanctions.
Tomlin insisted the incident was unintentional.
"As I stated yesterday, I take full responsibility for my actions and I apologize for causing negative attention to the Pittsburgh Steelers organization," Tomlin said in a statement Wednesday.
"I accept the penalty that I received. I will no longer address this issue as I am preparing for an important game this Sunday against the Miami Dolphins."