The 33-year-old fell out of favour at Stamford Bridge last campaign under former boss Rafael Benitez, but he is now back in the side as a regular following Mourinho's return to the club last summer.
The Portuguese coach admits that he has been impressed by Terry after the defender helped the Blues maintain their one-point lead at the top of the Premier League table on Saturday by scoring a late winner in their 1-0 victory at home to Everton.
"With me he has always played well, except when he had back surgery and lost an important part of the season," Mourinho is quoted as saying by Sky Sports News.
"But in my first two seasons here he had a fantastic level. Now? This season he is doing very well."
Terry has scored three goals in 32 matches for Chelsea this season.