Im a new player and I would like to ask if PK is possible outside of outlaw mode in chaos zones? 
cause I've been PK-ed many time while farming in chaos zones and Im not in outlaw mode.

Its not possible. If ur not in outlaw mode in chaos zone pk is not possible. Maybe your Guild was at war atm against an other guild. So they entcountered you and had gone for the kill.

It is possible that your guild might be in a guild war. Remind your guild leader to use the protection mode if they want certain members not getting involved in the war.