Jackson was out for Sunday's win against the Green Bay Packers after he was kneed in the back during the loss to the New England Patriots a week prior.
"He's coming off a very serious injury and he's working at it," said Harbaugh. "There was improvement throughout (last) week."
Baltimore will return to practice on Wednesday, December 31st, and an update will be provided on Jackson's status then.
Backup QB Tyler Huntley led the Ravens to another win in his second start of the season, the previous one being against the now-crowned NFC North champion Chicago Bears.
Huntley finished the win in Green Bay with 167 total yards and one touchdown, while completing 16 of his 20 passing attempts. In both of his starts this season, Huntley has put up 293 passing yards on 32-of-42 passing (76%) with two touchdowns, no interceptions, and 113 rushing yards on 16 attempts (7.1 ypc).
This Sunday night, the Ravens will be taking on the Steelers in the final game of the NFL regular season in a battle for the AFC North title and the final playoff spot.