how to remove focus

[Jiang XU <jiang xu echostar com>]

I wonder how to remove focus from a widget.
I try to make my program workd this:
1. when specified key is pressed, the specified widget is getting focus
by using gtk_grab_focus();
2. if a widget is focused, but when some invalid key is pressed, the
widget should leave focus, which means at this time, no widget is
focused.

So I wonder how to remove the focus from the widget?

If anybody knows, please tell me ASAP

Thanks