Can you post a picture of the set-up?
Really quick, here are some things off the top of my head that can cuase high humidity.
1) water dish. especially if it has a large surface area of water.
2) Poor ventilation such as a glass or plastic container with holes in it rather than a screen top to provide ventilation.
3) Live plants
4) Absorbant substrate. (If you're using paper towel or carpet, consider tile.)
5) Wrong temperatures.