The unrest erupted after federal officers nabbed a protester who appeared to be writing "RIP Dominique Dunn" on the court building, according to The Oregonian.
The paper estimated there were about 200 demonstrators at the site.
Dunn has been identified in social media posts as the black man shot dead at a strip club Thursday night.
A group called the Pacific Northwest Youth Liberation Front alleged the shooting was racially motivated — which police have denied — and urged demonstrators to gather, according to the newspaper.
Portland police tweeted Friday night they were aware of an arrest at the courthouse. The area has been the scene of demonstrations after George Floyd's death and they have sometimes turned violent.
Comment: From the same protest: