Darn hard to catch mice. They'll keep coming back. Usually mice are attracted to food - what are you feeding your rabbit? If what you're feeding your rabbit contains seeds and nuts, then the mice are probably attracted by that. Rabbits should be on pellets only, and trust me... mice aren't attracted to pellets, I've tried to get my own mouse interested, but he has none whatsoever.
Mice also like dark, sheltered, locations. Such as behind a litter box. Is the litter box in a corner of the cage that's next to a wall? Perhaps try moving it to where it's more out in the open.
Where's the cage located? Someplace quiet? Perhaps you could move it to a room that gets a lot of traffic. The mice won't feel nearly as obligated to stay in the cage if you do that - they want someplace that's quiet and hidden away. If there's always the noise of a TV, or people stomping around, chances are they won't feel inclined to make home in your rabbit's cage.