Another 10 people were wounded in the bombing outside the the National Defence Forces base in the Kurdish-majority city of Qamishli on the Turkish border, Syrian Observatory for Human Rights director Rami Abdel Rahman told AFP.
State television reported that there had been dead and wounded in a blast in the Hasakeh province city but made no mention of it being near the militia headquarters.
Syrian government forces largely withdrew from Kurdish-majority regions of the northeast and northwest in the middle of last year but have maintained a limited presence in some areas.
Their position has angered some rebels, who consider the Kurds regime allies for refusing to allow opposition fighters to operate inside their cities.
And jihadist groups, for whom the secular nationalism of Syria's most powerful Kurdish group, the Democratic Union Party (PYD), is anathema, have fought repeatedly with Kurdish militia in their bid to consolidate supply lines to neighbouring Iraq.