In videos shared on Twitter, a group of cars and pickup trucks adorned with large Trump flags can be seen riding alongside the Democratic campaign bus on Friday.
The footage shows the cars boxing in the campaign bus as it travelled from Antonio to Austin.
Mr Trump defended his supporters on Twitter, saying the “patriots” had done nothing wrong.
The president’s tweet came hours after the FBI confirmed that it was “aware of the incident and investigating”.
On Sunday night, Mr Trump retweeted a screenshot of the FBI statement, adding: “In my opinion, these patriots did nothing wrong.
“Instead, the FBI & Justice should be investigating the terrorists, anarchists, and agitators of ANTIFA, who run around burning down our Democrat run cities and hurting our people!”
In my opinion, these patriots did nothing wrong. Instead, the FBI & Justice should be investigating the terrorists, anarchists, and agitators of ANTIFA, who run around burning down our Democrat run cities and hurting our people! https://t.co/of6Lna3HMU
— Donald J. Trump (@realDonaldTrump) November 2, 2020
An FBI spokesperson said the bureau had no comment about the president’s tweet.
Mr Trump’s tweet come as tensions remain high between the president and FBI Director Christopher Wray.
The president has reportedly told people around him that he is frustrated with Mr Wray over the FBI director’s public statements on issues like voting fraud, Russian election interference and antifa, and has discussed the possibility of removing Mr Wray if he wins re-election.
Mr Trump has also pressed the Justice Department and FBI to act against his rivals, including Democratic presidential candidate Joe Biden himself.
On Saturday, Mr Trump tweeted a video of his supporters following the Biden campaign bus, adding: “I LOVE TEXAS!”
The Texas Democratic Party chairperson did not directly address the incident but said people should “ignore the noise and go vote”.
“Voting is the only thing that matters right now,” Gilberto Hinojosa said in a statement.
“We’ve never had anything like this. At least we’ve never had a president who thinks it’s a good thing,” Mr Biden said during a campaign event in the Philadelphia suburbs.