Answer:
Yes of course it is. Unless it is the Lien Holder selling the car or if the payment is being made directly to the lien holder.
Selling a car with a lien just because you have the title (Liened Tile) in hand is wrong and very unlawful even if the buyer knows it has a lien.
Do not give cash to someone selling a car with a lien, that is also illegal if you know they are not the lien holder. If the seller has a problem with you paying the creditor directly they are probably a crook!