It depends. If a character stops whatever he was doing whenever he sees you, and rushes towards you, then you KNOW you are being targeted.
However : 1. If he comes at you again and again and kills you, he's a bully and IS harrasing you.
2. And if he comes at you again and again but it is you who manage to kill him, he's a moron and is trying his best to harass you.
Its the situation no. 1 that is concerning.
On a more serious note, if someone kills you again and again, speak up. If he doesn't answer or answer bullishly, report him. Its as simple as that.