[RightDeve]

I wonder why no one bothered to reply this simple question..
Yes, it's obviously possible. You see some icons on the upper right of the screen when you're deploying them, there are those button to "plant" them, and there are those to "remove" them from a hex.
One tip for deploying mines; if you want your mines to be invisible to your opponent, plant them after the attacking player has finished his purchase of units. Otherwise, it'll become visible to both sides.

Cheers...