I have property that has a lien placed on it. Can I pay the mortgage off with a potential buyer, then transfer ownership to buyer?

 You do not state what kind of lien is on the property besides the mortgage.  A mortgage is a lien.  I will assume you speak of a tax lien or a judgment lien, and that it was placed on the record after the mortgage. If your buyer is prudent, he will have the title examined before the purchase and the lien (as well as the mortgage) will be discovered.  It will have to be paid along with the mortgage in order for good title to be passed from you to the buyer.  If your buyer is not prudent and does not have an attorney examine the title, and if you sell the property to him without paying the lien, and without informing him of the lien, the lienholder will almost certainly become aware of the sale and will cause the property to be sold to pay the lien.  If that happens, you can probably expect to be sued rather promptly.  Do not try to sell property that is subject to a lien without paying the lien off.