The 23-year-old is understood to be a target for new United boss Louis van Gaal, while Arsenal and Tottenham Hotspur are also said to be keeping tabs on him.
The Republic of Ireland international, who enjoyed a brilliant debut campaign for Everton after joining from Wigan Athletic last term, feels United's interest shows he is doing well.
"If a club like Manchester United are interested, obviously you are doing a good job," McCarthy told the Evening Standard.
"We will see what happens."
Tottenham are also being heavily linked and McCarthy says he came close to joining them ahead of Everton.
"Tottenham didn’t come up with the money but Everton did within the last couple of hours [before the transfer window closed]. Obviously it was just one of those things with Tottenham," he added.
McCarthy admits he was delighted with how last season went at Goodison Park.
"You would like to get into the Champions League but, thankfully, we've got the Europa League. People say the Europa League is not such a big thing but it was a massive achievement for everyone at the club," he said.
"Obviously, it will be a long season with the Europa League and I am sure the gaffer will bring in rotation. I'm looking forward to getting into the season and getting going again. It is a big season ahead.
"We are no different from any other club. Our main aim is to get into the Champions League. We want to improve on last season and push on even further."