If you want to suppress AdSense in a particular post or age, give the comment "<!--noadsense-->" somewhere in its text.

Or, insert a Custom Field with a key "adsense" and give it a value "no".

Other Custom Fields you can use to fine-tune how a post or page displays AdSense blocks:
Keys:
adsense-top, adsense-middle, adsense-bottom, adsense-widget, adsense-search
Values:
left, right, center, no