I have created this function in bp-custom.php page.
function filtering_activity_default( $query ) {
if ( empty( $query ) && empty( $_POST ) ) {
$query = 'action=activity_update,joined_group';
}
return $query;
}
add_filter( 'bp_ajax_querystring', 'filtering_activity_default', 999 );
This is working for me as expected.