My web application is extended with FBA authentication for External Users.  My requirement is in FBA authentication mode  people picker should show only FBA Users.it should not show Windows Users. 

In windows Authentication it should show Windows AD Users +FBA users.  This is working fine.

Here is my Web Application URLs:

FBA Authentication : http://Portal.FBA.com

Windows Authentication : http://portal.Internal.com

Thanks

You would need to remove Windows Authentication from the zone with FBA-only on it.