How can i list random author?

The Codex lists rand as the orderby string, not RAND. I suspect that either works but I haven’t checked. But that isn’t how I’d do this. I’d lean toward something like…

$current_category_ID = getCurrentCatID();
$current_cat_id = $current_category_ID;

$author_array = array();
$args = array(
  'numberposts' => -1,
  'cat' => $current_cat_id
);
$cat_posts = get_posts($args);

foreach ($cat_posts as $cat_post) :
  if (!in_array($cat_post->post_author,$author_array)) {
    $author_array[] = $cat_post->post_author;
  }
endforeach;

shuffle($author_array); // randomize

Database ORDER BY isn’t terribly efficient. ORDER BY RAND is especially inefficient. That code does the sorting in PHP on a smaller array, so it should perform better.