For PvE or PvP servers?
For PvP, any and all zones are PvP battlefields if one wants it to be.
For PvE, any Opposing NPC is a target. When an NPC is attacked by you, it makes you a target for PvP.
But if youre talking about PvE server PvP arenas... No, i havent heard about them on a full scale. Their is however duels.
You can challenge one player to a duel, which is like a one on one PvP. If you win, its announced that you won to the whole region and that the other guy lost. The other guy then has to bow to you, or kneel in front of you... one of the two.
Now count how many times ive said PvE or PvP in this message and win a cookie.