It should be moist but not dripping wet. If they are grubs, they will come to the surface normally every once in a while, unless the substrate is too dry/wet, they are hungry and don't like the substrate or the container is too small. Can also happen when they are getting ready to construct a pupal cell.
If they are adults, don't worry, they come to the surface a lot - and with Strategus, they will be really active in the early evening and will fly around in their container.