The eight were detained last week for "inciting hatred, violence and terrorism" against Jews and Israeli security forces, mostly with messages and videos on Facebook, a police spokesman told AFP.
The spokesman said one of the suspects had posted a picture of himself with an M16 assault rifle. Such postings had resulted in "many messages of support on Facebook," he said.
The operation was the Israeli police's "biggest aimed at repressing this kind of incitement to violence on social networks and the Internet," the spokesman said.
On November 18, two Palestinians armed with meat cleavers and a pistol attacked a Jerusalem synagogue, killing five people, before they were shot dead.