E! Online reported Friday that Pratt, actress Heidi Montag's boyfriend on the MTV series, has challenged Kutcher to a 30-day Twitter contest that will be decided by each contestant's final users tally.
The challenge from Pratt, 25, comes in the wake of Kutcher defeating the CNN cable TV network in a similar Twitter follower race.
MTV said Friday that Kutcher, star of movies such as "The Butterfly Effect" and "Just Married," had challenged CNN to a race for 1 million Twitter followers.
The 31-year-old actor managed to defeat CNN, reaching the designated tally a half an hour faster than the news network.
MTV said as part of his challenge, Kutcher donated $100,000 to the Malaria No More Fund, which buys mosquito bed nets for those living in areas filled with malaria-laden mosquitoes.