I've noticed that my back seems to sweat far more often than my head or armpits.
Just a few minutes ago, I jumped out of my chair and ran to the bathroom. Next thing I know, the back of my shirt is wet from back sweat. The really weird thing was I was rather cold.
Is this normal?
Unless you are experiencing odd hot/cold flashes and what not I wouldn't worry about it too much. Everybody is wired differently. I use to sweat way easier than others I knew, and I was always the skinny guy of the bunch. Your core is where most of your heat is anyhow, so if you are up against a chair back, it is likely insulating it and holding in heat.