BuddyPress.org

If you’re using WPMU or WP 3.0 in network mode, try this:
https://wordpress.org/extend/plugins/bp-registration-options/

The plugin author hasn’t updated this for single WP yet.

A more, manual method involves forwarding the activation emails to an admin account so you can approve them manually that way.

Put this sample code in your theme’s functions.php:
http://wordpress.pastebin.com/Qf2cskRj

Replace “get_site_option( “admin_email” );” with a custom email address if you don’t want it to forward to your admin email addy.