Mourinho was shown a red card in stoppage time after he appeared to make a gesture towards the Monza coaching staff.
"I don't know why I got the red card, I only made a gesture to the bench, not a single word," Mourinho said.
"The Monza bench put a lot of pressure on the referee; they shouldn't have behaved like that."
With the red card, Mourinho won't be on the bench for Roma's next league game, on the road against his former club Inter Milan.
Despite appearing to mock the Monza coaching staff, Mourinho was full of praise for the visiting team for their display with 10 men.
"They didn't deserve to lose the game," Mourinho said. "My team was always in difficulty, we made a lot of mistakes and we suffered. It was a game with a low technical level but a high emotional one."
After a poor start to the season, Roma have won three consecutive league games to leapfrog Monza into sixth place in the Serie A table.
Information from Reuters was used in this report.