Code snippet of navbar of bootstrap is show below:

<div>
<div>
<a href=”#”>Title</a>
<ul>
<li><a href=”Home.aspx”>Home</a></li>
<li><a href=”Page1.aspx”>Page1</a></li>
<li><a href=”About.aspx”>About Us</a></li>
</ul>
</div>
</div>

Now when user click on ‘Page1′, class of li associated with it is set to ‘active’.
jQuery to obtaing that behaviour is shown below:

<script type=”text/javascript”>
$(document).ready(function () {
var url = window.location;
// Will only work if string in href matches with location
$(‘ul.nav a[href=”‘ + url + ‘”]’).parent().addClass(‘active’);

// Will also work for relative and absolute hrefs
$(‘ul.nav a’).filter(function () {
return this.href == url;
}).parent().addClass(‘active’);
});
</script>

References:
1. http://twitter.github.com/bootstrap/components.html#navbar
2. http://stackoverflow.com/questions/11533542/twitter-bootstrap-add-active-class-to-li