If you enter any Java Script or HTML code in your posts, Blogger will automatically execute that code considering it a regular part of your post. We just need to encode our HTML special characters like <, >, & into entities <, >, &. This is a really painful process but Beta Templates is here to help you.
1- Go http://www.blogcrowds.com/resources/parse_html.php or to http://www.eblogtemplates.com/blogger-ad-code-converter/ paste your code in the box there and press CONVERT AD CODE button.
2- The page will refresh and you'll see that the code you pasted in the box has changed. Don't worry, copy that code and paste it in your post.
3- Publish your post and you'll see that your original code will appear perfectly without execution.
Tip: When you're trying to directly copy-paste Adsense code in Blogger HTML, you'll first need to convert it otherwise you might receive an error.