Highlight wp_nav_menu when category is selected

one solution to your problem using jQuery( put this code in functions.php )

<?php
add_action('wp_footer','ravs_browse_menu');
function ravs_browse_menu(){
 if(isset($_GET['cat']) && $_GET['cat'] !=''){
 ?>
 <script>
  jQuery(document).ready(function(){
   jQuery('#menu-item-299').addClass('current-menu-item');
  });
 </script>
 <?php
 }
}
?>