I don’t know if it’s normal, but I think it is. If a bunny pees repeatedly when you clean up his mess, I’d say that’s a territorial thing. My buns go in their boxes fairly often. I don’t know if it’s like with dogs, the dogs I’ve had have almost always pees/d several times during a walk, minutes between. When I put my Bam’s box on the floor to empty and refill, my other bunny jumps into it and immediately pees if he gets the chance (my buns are both neutered boys, but have no love for each other). Maybe they’re always saving a little bit of pee if they should need to mark sth?
Things to worry about regarding pee are straining to pee as in peeing very frequently with very, very little urine coming out, pee leakage resulting in pee on the inner legs so the bunny is always wet, madly excessive drinking that results in floods of pee, pee with flecks of blood in it (NOT red pee, red pee is perfectly normal in bunnies). Not that your bunny is showing any of those symptoms.
A bunny that gets lots of fresh vegs pees more frequently according to my observations.