Q : Is this possible to activate a feature, that they are no duplicate banner on WordPress, which means that they will never be the same banner of maybe different or the same zone will be shown together?
A : Add this line, document.write ('&block=1');
in the next line of document.write (\"?zoneid=". $zoneID ."\"); code on "openx-wp-widget.php" file from "OpenX WordPress 2.5.x widget" plugin.

Once you added this, duplicate banners will not visible on same page.