code in header.php

<!-- Primary Mobile -->
<nav id="primary-mobile" class="main-navigation" role="navigation">
	<h3 class="menu-toggle"><?php _e( 'Primary Mobile', 'twentytwelve' ); ?></h3>
	<div class="skip-link assistive-text"><a href="#content" title="<?php esc_attr_e( 'Skip to content', 'twentytwelve' ); ?>"><?php _e( 'Skip to content', 'twentytwelve' ); ?></a></div>
	<?php wp_nav_menu( array( 'theme_location' => 'secondary', 'primary-mobile' => 'nav-menu', 'fallback_cb' => false ) ); ?>
</nav><!-- #primary-mobile -->