It all depends on the terms of the auctions, but in most cases - no. You bid on the home and are provided with a special warranty deed which excludes the mortgage. You are provided clear title.
Sherriff or tax auctions are often different. You need to refer to the conditions of the auction, which are usually listed on the websites.
One thing to be careful of with auctions are the terms. You may be responsible for back taxes, mechanics leins, city violations, and even removing the current occupants - be it the former owner or tenant. You need to look at the terms very carefully.