Footage on social media showed protesters yelling at a large group of police officers forming a line outside Parliament House about 11am on Thursday.
As protesters drew closer to the barrier a physical clash erupted with officers forcibly separating members of the protest group.
The protesters are connected with sovereign citizen and anti-vaccination movements, which have repeatedly held protests outside Old Parliament House in recent weeks.
Police clash with protesters outside Parliament House
Videos posted on social media included showing one protester shouting “always was always will be traditional sovereign land”.
In a statement an ACT Policing spokesperson said authorities "responded to a group of people attempting to enter Parliament House to protest unlawfully”.
The social media footage also showed protesters pouring water over themselves following the use of the pepper spray.
Police are closely monitoring the activities of the group in the lead up to January 26 when Australia Day is recognised.
It's understood some of the protesters have been camping near Old Parliament House.
But groups linked to the Aboriginal Tent Embassy located opposite this site have condemned their behaviour and stressed they are not associated with them.
Separately, two men have been arrested over alleged involvement in a fire at Old Parliament House on 30 December, the force said.
A 30-year-old from Bourke, NSW, has been charged with aid/abet arson of a building, deface public property, aiding and abetting the damage of property, assaulting a frontline service worker and resisting a territory public official.
A 38-year-old from Lindendale, NSW, has been charged with assaulting a frontline service worker, obstructing a public official and breach of bail.
Both are due before the ACT Magistrates Court on Friday.