The man accused of an arson attack on the Canberra headquarters of the Australian Christian Lobby (ACL) will plead not guilty on the grounds of mental impairment.

Jaden Duong, 36, was badly burned in the incident and is facing charges of arson and property damage.

The explosion, which took place in December 2016, occurred after the man allegedly blew up gas cylinders inside a van, damaging the vehicle and gutting the ACL office.

The Australian Christian Lobby headquarters in Canberra was extensively damaged in the 2016 incident. ( ABC News: Ian Cutmore )

At the time investigators said they did not believe the incident was terrorism related or politically motivated.

His lawyers told the ACT Magistrates Court his involvement was not in issue, but he would plead not guilty citing mental impairment.

Duong did not appear in court for the first mention of the case.

Prosecutors asked for strict bail conditions but Magistrate Robert Cook refused since Duong was not present.

The case will return to court in August.