"Chelsea are the champions and one of the top teams in the country and I consider them - and they consider themselves, too - a big contender for the title," he told Sky Sports.
"I think six (teams are competing for the title) because Everton, in spite of their huge investment, didn't manage to follow the group.
"I think in the table now you can already feel the four or five are there. If Liverpool are a couple of points behind I'm pretty sure in a couple of weeks they'll be close to us too."
Juan Mata and Nemanja Matic will return to Stamford Bridge this weekend, and Mourinho remains shocked that United were able to sign the Serbia international in the summer, the midfielder having impressed at Old Trafford since his £40 million move.
"I was surprised when [Matic's] agent called me to say 'do you want him?' " Mourinho added.
"I was surprised, but he's an agent I know well. Normally he's very direct and objective, he doesn't waste time, he doesn't try to get people to be interested in his players to improve their situation at their club.
"Normally he's very straightforward, so when he told me 'you can have him if you want', of course I want."