authentication issues

Every time I go to move a document anywhere ( ex. moving a document from the desktop to the HD folder) I get a screen saying that "Modifying Macintosh HD requires an administrator name and password." I then need to click on "Authenticate" and type in my password. This is a computer I use at home and am the only one using it (I am the Administrator). How do I stop having to authenticate every time I want to move anything anywhere??