Get_Category Not Working

Here’s the site: http://www.gardenveg.co.uk/

Basically, if you click on any of the categories, there is a box at the top. I want to list the name of the category and the category topic.

However, for some reason, there seems to be a problem. It is not ALWAYS displaying the correct category.

Please help. Here is the code:

<div><h2>You are Currently Browsing</h2> <h1><?php
$category = get_the_category();
echo $category[0]->cat_name;
?>:</h1> <h3><?php echo category_description(); ?></h3></div></div>