Exclude stylesheet from admin

There are a couple of options. One is to wrap the enqueue in a check to see if it is the admin.

if(!is_admin()) 
    wp_enqueue_style(....);

The other is wait to enqueue the style until template_redirect.

function my_enqueue_styles() {    
    wp_enqueue_style(....);
}
add_action( 'template_redirect', 'my_enqueue_styles' );