As long as the paint on the wall isn't peeling off or flaking then yes you can apply the wallpaper paste to the wall with the paint and then apply the wallpaper over the painted wall without a problem.
There's no need to strip the paint off the wall before applying the wallpaper just make sure the wall is clean and then apply the wallpaper paste and apply the wallpaper making sure to get any air bubbles out of the paper as you go along.