Ferguson retired in 2013 as the club's most successful manager.
The 74-year-old Scot had stayed away from Carrington since then.
"He had not been back since he left, but I brought him back to be with his people," Mourinho told the United We Stand fanzine (subscription required).
"I wanted the players to see the big man and for me and him to share some minutes and have lunch together. I enjoyed it, he enjoyed it."
In his 26 years at Old Trafford, Ferguson led United to 13 league titles, two Champions League crowns, five FA Cups and four League Cups.
"I'm the type of person who does not see ghosts. I respect the past and I know he loves the club," said Mourinho, who was appointed in May as the third manager to succeed Ferguson after David Moyes and Louis van Gaal.
"We have good relations and I know this is his house.
"When he wants to come here, to the dressing room, to see the players train, he knows he is more than welcome."
Mourinho also said there was more expected of teenage forward Marcus Rashford in the current campaign after the 19-year-old's successful breakthrough last season.
"Last season there were no senior players on the bench waiting for him to make a mistake. The choice was Rashford or Rashford," he added.
"The situation is different this season. The number of injuries is smaller. The expectations about the players is higher.
"[Former United winger] Ryan Giggs' second season [1991-92] was not comparable to the season when he started. Then, in the third season, he reached the level of Giggs. It was the final explosion of Giggs. We want to play young players but sometimes in football, it is about the moment."
Manchester United manager Jose Mourinho has revealed former boss Sir Alex Ferguson has been back to the club's Carrington training ground several times this season.