River Williams, 28, was arrested on Saturday and later taken to the Alexander Maconochie Centre, from which he appeared via phone in the ACT Magistrates Court on Monday.

He denied that he was in fact River Williams, telling the court that name was "a dead entity under your realm".

As Chief Magistrate Lorraine Walker read five charges, including allegations of joint commission arson and assaulting a police officer on December 30 last year, Mr Williams spoke over the top of her.

"I'm just wondering how any of this has any standing if you haven't proven your national sovereignty," he said, adding that he had his own laws and did not "stand under this law".

Ms Walker had her associate briefly mute the 28-year-old in order to stop him interrupting proceedings.

Once she had finished reading the charges, which also included allegations of attempting to hinder police, resisting police and failing to attend a January court date as required, bail was discussed.

The 28-year-old said he did not understand why he had to apply for conditional liberty, prompting Ms Walker to tell him he would be remanded in custody to "sit at the AMC" if he chose not to.

In light of this, Mr Williams said he wished to speak to "a guy who wants to give me legal help".

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He added that he was epileptic and that "my mind isn't thinking straight at the moment because of [a] seizure I had earlier".

Not long after this, he disappeared off the phone line after saying: "I'm about to have a seizure, I think."

The case was stood down for more than an hour during the court's lunch break, after which time Mr Williams was dialled back in.

He represented himself as he applied for bail, telling the court he had been "spewing" and still felt unwell.

Prosecutor Archita Sreekumar opposed the 28-year-old's release, arguing Mr Williams was likely to commit offences and fail to appear in court as required if he was released.

Mr Williams countered that he "definitely" would not commit crimes and said he was "happy" to attend court, claiming he had only missed the January date because he had "lost the paperwork".

Asked by Ms Walker about his response to the charges, the 28-year-old said he "didn't have anything to do with the fire".

He also said he had linked arms with other people outside Old Parliament House, but "I definitely didn't assault anyone".

The court heard one of the charges arose from a subsequent incident on January 14, when officers cleared a campsite where anti-government protesters had been staying.

Mr Williams, who is said to have been lying down on a tent to prevent its removal, denied doing this.

Ms Walker therefore entered not guilty pleas to all charges except the failing to appear allegation, on which there was no plea.

She ultimately decided to grant the 28-year-old bail to live at an address in Forbes Creek, not far from the ACT.

While on bail, Mr Williams must report to Braidwood Police Station weekly and only enter the ACT for court appearances and pre-arranged legal appointments.

He is due back in court on June 6.

Several other people have already been charged over the December 30 fire at Old Parliament House, which sustained damage with an estimated repair bill north of $4 million.

The blaze occurred in the midst of anti-government protests, during which aggrieved people were attempting to evict officials from public buildings.

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