The protesters are holding Kurdish, Armenian and US flags and are shouting slogans critical of Turkey.
Some are carrying banners that say "Erdogan is Not Welcome", "Recognize Genocide", "Out of Rojava" and "We Support Our Friends - the Kurds".
The protest is peaceful and there is no increased police presence in the area.
Erdogan and Trump are expected to discuss the situation in Syria, the Russia-supplied S-400 air defence systems to Turkey and the F-35 fighter jet programme, among other issues.
Last week, the two leaders confirmed over the phone the meeting will take place given that Erdogan’s trip was uncertain amid growing tensions between Turkey and the United States following the Turkish military offensive in northeast Syria last month.
Turkey's purchase of S-400 air defence systems, US congressional resolutions on the Armenian genocide and sanctions against Ankara have also contributed to the escalation in tensions between the two countries.