A man in a blue sweater was tackled before being escorted out by law enforcement before being held in a bathroom inside the venue.
When Trump returned to the stage, he thanked the Secret Service.
"Nobody said it was going to be easy for us. But we will never be stopped. Never ever be stopped. I want to thank the secret service. These guys are fantastic. They don’t get enough credit," Trump said.
The Secret Service released a statement saying that the commotion started when someone in the rally shouted "Gun," but said that no gun was found.
"Immediately in front of the stage, an unidentified individual shouted 'gun.' Secret Service agents and Reno Police Officers immediately apprehended the subject. Upon a thorough search of the subject and the surrounding area, no weapon was found," the statement said.
The Secret Service and the Reno Police Department were investigating the incident, the statement said.
When contacted by ABC News, Reno Police Department said that they had little detail, only that they had initially been informed that there was a "medical incident" that precipitated the commotion.
Trump now heads to Denver, Colorado, where he was scheduled to host his fourth rally of the day.
ABC News' Dean Schabner contributed to this report.