The people at Westminster Magistrates' Court are holding up banners saying "Don't Extradite Assange" and "Free Assange".
The session later on Monday is expected to be of a technical nature — to determine the agenda of future hearings on Assange's potential extradition to the United States.
Graffiti picturing Assange as a saint has appeared in London.
Assange is currently serving a 50-week sentence in London's Belmarsh prison over violating his bail conditions. In the United States, he is facing espionage charges over his work with WikiLeaks that published a large number of leaked classified documents.
The Wikileaks founder was arrested in London in April and sentenced to 50 weeks in prison for jumping his bail back in 2012 when he took refuge inside the Ecuadorian embassy in the UK capital to avoid extradition to Sweden, where he faced sexual assault charges, and possible extradition to the United States.