Select the paragraphs before and after the line. On the Home tab of the
ribbon, click the arrow on the Border button (in the Paragraph group), and
then choose "No Border."
If you want to turn off the feature that created the line, do the following:
Click the Office button, and then click Word Options. In the Proofing
category, click AutoCorrect Options. On the AutoFormat As You Type tab of
the dialog box, clear the "Border lines" option. Actually, you may want to
clear most options under "Apply as you type" and "Automatically as you
type"; see
http://word.mvps.org/faqs/formatting/TameAutoFormat.htm.
