The Old Trafford outfit begin their campaign on Tuesday, hosting Swiss side FC Basel in the opening group stage match.
"Being back in the Champions League is going back to the natural habitat. Manchester United (have been there) season after season," Mourinho told reporters. "Motivation is very high."
"We have to try to go to the last 16 and enjoy that special knock-out phase with the best teams in Europe."
The Portuguese boss believes his team are in good form after starting their league campaign with three wins and a draw.
Mourinho says he loves the packed Christmas schedule that English teams have and believes they cannot use the busy schedule as an excuse for poor Champions League performances.
"We have no winter break, and in other countries there is a winter break, but that's cultural - it means a lot, and I have to admit I love it," he added.
"But no complaining this is what we have, we have squads and if we think they're tired we play with other players."
Mourinho also said he was not surprised by the sacking of Crystal Palace manager Frank de Boer after just four league games in charge.
"In football, nothing surprises me. I was sacked as a champion, (Claudio) Ranieri was sacked as a champion, Frank de Boer is sacked after four games," Mourinho said. "Next season something incredible will happen again."
Defenders Eric Bailly and Phil Jones are serving suspensions and will be replaced by Chris Smalling and Victor Lindelof at the centre of defence for Tuesday's game, while midfielder Marouane Fellaini is a doubt as he recovers from a calf injury.