You'll find its either her asserting dominance or she is on heat/wanting to have babies. My girl bunny acted like this just before she feel pregnant, it might be like a type of mating call to him saying "I'm ready now!"
Are you really sure you want them to breed? I was the same as you but its quite traumatic finding suitable homes for the babies, and bear in mind that as soon as she gives birth she will get pregnant again the same day.
So as soon as you notice signs of pregnancy (which arent always very obvious until the birth) I would get your boy un-boyed straight away to avoid two consecutive litters which can be very stressful on little girl bunnies health.
just a friendly word of advice!