Church leaders charged with trespass after a sit-in protest at the electorate office of Foreign Minister Julie Bishop have been given spent convictions.

Eight ministers from various Christian church groups were arrested for staging the sit-in at the Subiaco office of Ms Bishop on December 10.

The ministers, who were protesting about children being kept in immigration detention, were charged with trespass after the incident.

Earlier today, about 60 people held a rally outside the Perth Magistrate's Court, protesting against the church leaders' arrest.

The ministers claimed they were arrested, locked up and strip-searched by police before being charged with trespass.

After the court ruling, the protesters stripped to their underwear and started marching back to Ms Bishop's office in Subiaco from court.

A spokesman for the group, Allan McGrechan, said the detention of children was wrong.

"We are asking for the release of children in immigration detention and for more humane policies around refugees and asylum seekers," he said.

"Children in detention I think is very inhumane ... every day that they are locked up in immigration detention they have no hope of a better life."

Mr McGrechan defended the sit-in at the Subiaco office of Ms Bishop.

A rally protesting the arrest of the church leaders was held outside the Perth Magistrates Court earlier today. ( ABC News: Graeme Powell )

"We've written many letters to MPs, tried to get meetings with other MPs and at this stage we see there may not be any other way to draw attention to the inhumane treatment of refugees and asylum seekers," he said.

Pastor Jarrod McKenna of WestCity Church of Christ said instead of strip-searching church leaders, the nation should be "searching its heart for a humane response to those seeking safety".

"Today we call on the Government to make a public commitment to release the 135 children currently imprisoned on Nauru," Pastor McKenna said.

"These children have been cruelly shipped off, locked up and left in limbo, deprived of their precious childhoods."

West Australian Greens senator Scott Ludlam and state Labor senator Sue Lines also attended the protest.

"I have great respect for their courage to not be silent and I am proud of their action to stand up for refugees seeking asylum in Australia," Senator Ludlum said.