Unlike preg_replace, mb_ereg_replace doesn't use separators
Exemple with preg_replace :
<?php $data = preg_replace("/[^A-Za-z0-9\.\-]/","",$data); ?>
Exemple with mb_ereg_replace :
<?php $data = mb_ereg_replace("[^A-Za-z0-9\.\-]","",$data); ?>