This happened to me a couple of years ago in west TN:
Last weekend of the season, we were heading to the farm with doe tags in hand. Decided to hunt around the cabin we stayed in and let everyone else get in the stands. Super cold morning in the low 20's, high-teens. Ended up getting caught out in the open by a group of does. Sitting on my butt in the open field I steadied and pulled the trigger on the biggest doe, CLICK is all I heard. Calmly ejected what I thought was a bad round and chambered the next. CLICK again! repeated the same deal and chambered round #3. When I pulled the trigger:CLICK. I thought, "what in the heck is going on". I was holding the gun with the barrel pointing up, and all of the sudden BOOOOM! My gun went off without a finger near the trigger. What I think happened is that I had the gun in the cabin with me and when I went in the cold air, the condesation built up around the firing pen and had it frozen. It had obviously become unfrozen when it went off. I took that instance as warning to never leave my gun in the house on cold nights. But I'm gonna watch tonight and see what they say. I have never had a problem since and over 50 deer have fallen to that rifle including the 4 does I ended up taking that day.