Yes.
Edit ~/.kde4/share/config/kdesurc and set “Keep” to false.
If the file doesn’t exist, create it with this content:
[Passwords]
Keep=false
To do the same for all users, create a file /etc/kde4/share/config/kdesurc with that content.
But be aware that this only sets the default. An existing ~/.kde4/share/config/kdesurc will override this.