The 28-year-old actor - who stars as the Doctor in the BBC1 show and on BBC America - revealed the fans' reaction to his arrival at the comic fan convention in San Diego, California, was "exciting".
He told USA Today: "It's been completely overwhelming. It's exciting for us to be growing so much In America."
Matt was also joined by co-star Karen Gillan - who plays his time-travelling companion Amy Pond in the series - at the event, which featured a trailer for the second half of the programme's sixth series.
The crowd erupted with applause when they were shown the broadcast, which revealed the show's forthcoming episodes are set to return to the BBC on August 27 - and they could feature a darker version of the Doctor.
Matt added: "There's a lot of blood on the doctor's hands. If he stopped, he'd have to contemplate losing all these people."