Is there any way to restrict everyone's read permission of a particular namespace in mediawiki ?
Restricting read permissions granularly is tricky in MediaWiki, but possible. If you have only one namespace and one group ("everyone") to restrict, the Lockdown extension will do. Download the extension, then in your configuration:
require_once "$IP/extensions/Lockdown/Lockdown.php";
$wgNamespacePermissionLockdown[NS_PROJECT]['read'] = array('user');
$wgNonincludableNamespaces[] = NS_PROJECT;
(for the "Project:" namespace).