Abdallah Abu Rahma, 39, was one of the organisers of the weekly demonstrations against the barrier being built by Israel in the West Bank.
Protests are regularly attended by hundreds of Palestinians and foreign supporters.
They are largely non-violent, but are sometimes marred by Palestinian stone throwers.
Israeli forces fire stun grenades, tear gas canisters, rubber bullets and, sometimes, live rounds at the protesters. Several demonstrators have been killed and hundreds injured.
Abu Rahma was also fined US $1,200 (£760). He has already served 10 months in jail.
'Human rights defender'
The prosecution of Abu Rahma has been widely criticised by human rights groups.
And the European Union's foreign affairs chief Catherine Ashton has issued a statement in August saying: "The EU considers Abdallah Abu Rahma to be a human rights defender committed to non-violent protest… The High Representative is deeply concerned that the possible imprisonment of Mr Abu Rahma is intended to prevent him and other Palestinians from exercising their legitimate right to protest against the existence of the separation barriers in a non-violent manner."
Israel says the barrier was established to stop suicide bombers entering from the West Bank.
But Palestinians point to its route, winding deep into the West Bank around Israeli settlements - which are illegal under international law - and say it is a way to grab Palestinian territory.
In 2004, the International Court of Justice in The Hague issued an advisory ruling that the barrier was illegal and should be removed where it did not follow the Green Line, the internationally recognised boundary between the West Bank and Israel.