Rooney, 31, apologized this week after being pictured looking the worse for wear as he mingled with guests at a wedding party at the England team hotel last weekend.
Mourinho said Rooney was fit to face Arsenal on Saturday after withdrawing from England duty with a minor knee injury but did not want to discuss the specifics of what had happened.
"Over the last two, three days, nothing happened. He trained like everybody else, he wants to plays like everybody else," Mourinho told reporters at the United training centre west of Manchester.
"He's ready. What happened in the national team happened in the national team. I don't comment. "My players, when they go to the national team, they belong to the national team.
"What happens there for good, for bad I don't interfere and I don't like to comment." Some media reports suggested Mourinho had been unhappy with the Football Association for not supervising Rooney more closely after England's players were given a night off last Saturday.
But he said he just wanted to draw a line beneath the affair. "Sometimes they come back stronger than when they left us because something positive happens there; good performances, good results," Mourinho said.
"Other times, injuries, sometimes big injuries. Other times frustrations because they didn't play, because the result was bad.
"In this case we know what didn't go well, but the national team is a different chapter and a chapter that is closed now until March or the end of February."
Rooney played in England's 3-0 World Cup qualifying win over Scotland last week, but was withdrawn from the squad due to a knee injury and missed Tuesday's 2-2 draw with Spain.
He has struggled for playing time for United of late, although he started their last two games prior to the international break.