An FBI spokesman said they were responding to the incident and that the agent had shot and killed the man "while conducting official duties".
NBC News quoted unnamed sources as saying the suspect had tried to attack an agent.
Tsarnaev died in a shootout with police days after the deadly marathon blasts.
Anonymous law enforcement officials and a friend of the man in Orlando said he had been killed on Tuesday night.
FBI spokesman Dave Couvertier said in a statement: "The agent encountered the suspect while conducting official duties.