Talking to French television programme Telefoot (via Sky Sports' Rory O'Callaghan), the Portuguese manager said he is "sure" he will not retire at United as he has other ambitions he wants to fulfil: "What I can say is that I am still a manager with questions, with ambitions, with a desire to do new things, and I do not think...I am sure that I will not finish my career here."
Mourinho, 54, penned a three-year deal when United appointed him as Louis van Gaal's successor in May 2016.
The Sun's Neil Custis recently reported Mourinho will be offered a new five-year deal worth £65 million after United's impressive start to the new season.
Mourinho has historically only stayed at clubs for short periods while being successful.
He has won major trophies in charge of Porto, Chelsea, Inter Milan and Real Madrid but has only lasted more than three full seasons at a club on one occasion (his first spell at Chelsea, which ended one month into his fourth campaign in charge at Stamford Bridge).
Mourinho may yet stay longer than that at United, but it is clear he has other aims beyond his time with the Manchester outfit.
As O'Callaghan noted, he has previously expressed a desire to manage Portugal.