functions.php

<?php

/**
* Exclude Category from Blog
*
* @author Bill Erickson
* @link http://www.billerickson.net/customize-the-wordpress-query/
* @param object $query data
*
*/
function be_exclude_category_from_blog( $query ) {
	if( $query->is_main_query() && $query->is_post_type_archive( 'events' ) && !is_admin() ) {
		$query->set( 'category__not_in', array( 12, 34, 47 ) );
	}
}
add_action( 'pre_get_posts', 'be_exclude_category_from_blog' );