Albion were leading 1-0 when Mooy picked up two quick yellow cards, one for kicking the ball away, and another for a foul on Villa talisman Jack Grealish.
The Australia international said, “I’m really annoyed with myself and sorry, as I feel I’ve let my teammates and the fans down.
“The first yellow was just an instinct. The ball wasn’t where the foul took place, and I rolled it back to the position of the foul.
“For the second, I genuinely felt I could make the tackle, realised I couldn’t and tried to pull out, but it was too late.”
Mooy, following an excellent performance in the 3-0 win over Tottenham Hotspur, had been instrumental in an impressive start by Albion, and they led through Adam Webster’s first-ever Premier League goal.
Meanwhile, Albion boss Graham Potter had no complaints over referee David Coote’s decision, but also said Mooy had no reason to apologise.
Potter said, “It’s part of the game. Players make decisions, make mistakes and that’s how it is — we have to stay together and respond together, and that’s what we did.”
Mooy will miss next week’s visit of Everton to the Amex, as he serves a one-match suspension.