Trump briefly ducked at the podium and four Secret Service members scrambled to surround him after a man charged the stage at Dayton International Airport in Ohio.
Officers then grabbed the man, dressed in a black T-shirt and jeans, before he was able to reach the stage and hauled him away, Reuters reported.
"I was ready. I don't know if I would have done well but I would have been out there fighting, folks," Trump told a rally later in the day. He said the man "was looking to do harm."
The incident further increased tension after Trump's Chicago rally was scrapped amid chaotic scenes on Friday.
Trump's Republican rivals hurled scorn at the New York billionaire, saying he helped create the nervous atmosphere that is now sweeping the race for the White House with his fiery rhetoric.
Trump blamed supporters of Democratic candidate Bernie Sanders for the incidents in Chicago, where scuffles broke out between protesters and backers of the real estate magnate.
The scenes in Chicago followed a series of recent incidents of violence at Trump rallies, in which protesters and journalists have been punched, tackled and hustled out of venues, raising concerns about degrading security leading into the November 8 election.