Warm Floor

I noticed the floorboard of my Tahoe on the passenger side was warm. My wife and I went to dinner and she put her purse on the floor on the passenger side. When we got to dinner, she picked it up and noticed the bottom of the purse was warm. I put my hand on the floorboard and noticed the floor was rather warm. Does this mean the Cats are going bad or is this normal. It is a 99 Tahoe 4wd and 4 doors. The drivers side seemed OK. If it is bad, how do I check?