Police said they attended an "incident" on Northbourne Avenue in Civic at about 11.45am on Tuesday.

"The circumstances of the incident are currently being investigated," a spokesperson said.

In a video posted on Twitter, some protesters can be seen yelling at and filming the driver of a stopped public bus. Chanting of "let's stop the jab" can also be heard.

A spokesperson for Transport Canberra City Services confirmed they were aware of the incident and would also conduct a review into what had happened.

"The driver has been offered appropriate support by Transport Canberra representatives," a spokesperson said.

The group first attended Canberra in late January and early February, in the lead-up to a protest outside of Parliament House which saw a peak of about 10,000 people.

The demonstrators are made up of loosely affiliated sub-sections which include sovereign citizens, anti-vaccine conspiracists, evangelical groups and members of the far right, but say they are demonstrating together against vaccine mandates.

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The group largely dispersed after February 12, but police expected they would return for the handing down of the federal budget on March 29.

About 100 protesters gathered in Glebe Park at about 11.30am on Tuesday, before marching and driving down Northbourne Avenue to Parliament House.

Police said they diverted protesters' vehicles from certain roads as they moved towards Parliament House, and that at about 2.30pm some vehicles parked on grassed areas in front of the building were moved on, "however a small group of compliant protestors remained".

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