Mourinho has been questioned as a result of Tottenham's recent poor run of form but Son has rejected claims that some at the club are unhappy with the manager.
The South Korean forward said: "The rumours are just rumours. Our changing room has been fantastic.
"Obviously it depends on the results. I'm very sad if we lose and happy when we win. It's like everyone else. The mood went down when we had a couple of bad results but the dressing room hasn't changed. Everyone is happy and having a laugh and focused on every game. It is a bad rumour."
It has been speculated that Son may sign a new contract to commit his future to Spurs but the player is keen to focus on what is happening on the pitch for the time being.
He said: "I think it is a bit unfair to speak about a new contract at the moment.
"Obviously I am focused at the moment on my games, my team. I think this is the most important at the moment. I am happy to be here. I am working hard as a player, as a team and like I said before it is a bit unfair to speak about a new contract."
Son added that the "happiness" he gets from football has helped to keep him going during a demanding campaign.
Asked if he was feeling fatigued, Son said: "What should I say? If I say no it is probably a lie because already we play so many games but I said before, football gives me love, football gives me happiness."