Note: There\'s a very similar question, but it\'s WPF-specific; this one is not.
How can I determine if the current application is activ
since it's likely that some element in your UI has contain focus for the form to be active try:
this.ContainsFocus
http://msdn.microsoft.com/en-us/library/system.windows.forms.control.containsfocus(v=vs.110).aspx