Somehow, I activated the on-screen keyboard (Onboard) in the unlock screen and I can't deactivate it now. I've restarted the computer, but it's still there in the unlock screen.
How can I deactivate the on-screen keyboard in the unlock screen?
Search for Onboard settings from the gnome-shell overview.
Under General tab and Desktop integration heading, uncheck the option Show Onboard when unlocking the screen.
Run the following command in a terminal:
gsettings set apps.onboard xembed-onboard false
If the above is not working, try this one:
gsettings set org.gnome.desktop.screensaver embedded-keyboard-enabled false
worked for me (Ubuntu 12.04).