If they are only 6 weeks old (which is earlier than suggested for being separated from their mother) they are probably just playing. It sounds like you have a male and a female, but in any case, you will need to separate the bunnies before they are 12 weeks old to prevent litters and to prevent the fighting and injuries that can occur when they reach puberty. When you separate them, make sure that their cages or pens aren’t right up against each other. Rabbits have been known to make through cage bars, and they can also nip noses or ears if they can reach the other.
It may be best to go ahead and separate them now, in case they are older than you think. Otherwise you could let them stay together for another 2 or 3 weeks before putting them in separate pens. I’m really not sure if it’s best to separate them from the beginning or let them stay together for a little while since they are in a new place and may need some comfort. You definitely should separate them if the chasing looks like it’s getting aggressive. You can keep them in the same room near each other when you do separate them.