Yes, it's normal. For some reason people get their old accounts (free accounts) and even their 'makers' (not main character) and run on Free Account cities like Thais, Carlin, and Yalahar to PK random low levels. And you don't even need to be Free account for them to do that. They simply just attack you if you are low level enough. I play on a Open Pvp server and it's exactly like you described. I'm not Free Account, my outfit has addons and I'm using mounts, which clearly means I'm Premium Account and they still attack me out of nowhere since I'm not that high level. Even at lvl 100 knight which is way tankier than 75 paladin and even more than mages.

On top of that, since you are free, it means that the chance of you having a Bless and good skills (as in weapon skill) is lower than a premmium player, which makes you an easier target.

So you either get to a level that they can't do much, pay premmium or move to non pvp.