get_acf_field_group.php

function my_acf_get_fields_in_group( $group_id ) {
    $acf_meta = get_post_custom( $group_id );
    $acf_fields = array();

    foreach ( $acf_meta as $key => $val ) {
        if ( preg_match( "/^field_/", $key ) ) {
            $acf_fields[$key] = $val;
        }
    }

    return $acf_fields;
}

Thanks