Obama will be in Denver later this week to accept the Democratic nomination for president.
FBI spokeswoman Kathy Wright confirmed the FBI was investigating the reports but declined to elaborate. The Joint Information Center -- a command set up by Denver, state and federal authorities to field media inquiries during the Democratic convention -- said it had no immediate comment.
Tharin Gartrell, 28, was arrested during a traffic stop early Sunday by police in the eastern Denver suburb of Aurora. In his truck, officers found two rifles, including one with a scope; a bulletproof vest; boxes of ammunition; walkie-talkies; and suspected narcotics, said Aurora police Detective Marcus Dudley.
Police alerted federal authorities, who soon arrested Nathan Johnson, 32, at a hotel in Denver, Dudley said. A third man, Shawn Robert Adolf, 33, was arrested at a suburban Glendale hotel, Dudley said.
Adolf allegedly tried to escape officers by jumping from a sixth-floor window. He was hospitalized and was being held on $1 million bond for several outstanding warrants involving drug charges. Johnson also was being held on drug charges and his bond was unknown, Dudley said.
It wasn't known if the three men had attorneys, Dudley said.