The United striker was sent off on Friday evening for kicking out at Montenegro centre-back Miodrag Dzudovic.
In the wake of his dismissal and the recent arrest of his father in connection with a football betting scam, a number of reports have questioned Rooney's state of mind.
However, ahead of his side's trip to Liverpool on Saturday afternoon, Ferguson does not expect that Rooney's early season form will be affected.
"Obviously, he'll be disappointed," said Ferguson. "I didn't see it but it was only a reflex action by the boy. He's been tackled and reacted. He's got a fiery temper and, to my mind, it's not the worst thing in the world.
"I think we [channel his natural aggression positively]. He's shown tremendous improvement in terms of temperament and his reaction to tackles over the last few years.
"Maturity comes along and brings other things, it brings a responsibility which he's improving all the time."
Rooney has become the second player, alongside David Beckham, to have been red carded for England on two occasions.