I don't think it's allowed, but I don't see any suggestions of how we can prevent this. If this becomes a rule people will just go to a cave or some random spot and start farming secretly.
Maybe there should be a function where if one person has killed another person for like 10 times in less than 5 minutes the person he killed should be immune to his attacks. Doesn't matter if he runs off and kills another person, the person will still be immune. Of course the guy farming can probably get another guy to come and farm with him but I don't think my idea will do much and might change PVP in the wrong way.