highlighting the selected object

how can i highlighting the selected object when i move the mouse pointer over it

First of all, PLEASE read the tutorials!
Tutorials: http://www.ogre3d.org/tikiwiki/tiki-ind ... +Tutorials
"Intermediate Tutorial 3" shows how to draw a selection rect.
And the highlighting: Just change the material/texture and there you go. Or outline the model using a shader: http://www.ogre3d.org/tikiwiki/tiki-ind ... e=Cookbook or http://www.ogre3d.org/forums/viewtopic.php?f=5&t=51319

All untested, but it should work.