This error generated due to mysql  module not configured in your php . To verify this can use the function get_loaded_extensions(); . So, Create a file with name of exetension.php add below code  and execute.

<?php
 $arr=get_loaded_extensions();
 echo '<pre>EXTENSIONS - ';print_r($arr);echo '</pre>';
 ?>

 Output :
=======

 <pre>EXTENSIONSArray
     [0] => libxml
     [1] => xml
     [2] => wddx
     [3] => tokenizer
     [4] => sysvshm
     [5] => sysvsem
    ...
    ...
     [30] => pcre
     [31] => openssl
     [32] => dbase
     [33] => gd
     [34] => mysql
     [35] => mysqli
     [36] => PDO
     [37] => pdo_mysql
     [38] => pdo_sqlite

It will shows you list of loaded modules,  If you  could not found the line number [34] => mysql or [35] => mysqli  better you can trying to uninstall existing php & mysql and install yum  install php mysql.