A family of Microsoft word processing software products for creating web, email, and print documents.
The AutoFormat As You Type option (shown in the AutoCorrect dialog box) will only control automatic insertion of borders, for example, when you type three asterisks and then press Enter. You can't use the option to remove existing borders.
To remove an existing border, use the Borders and Shading dialog box. See the screen shot below.
Display nonprinting marks, for example by clicking the ¶ icon on the Home tab. Select the paragraph mark that is immediately below the table. Then go to the Home tab on the ribbon, click the arrow on the border button (in the Paragraph group) and then click Borders and Shading. In the dialog box, go to the Borders tab, make sure that "Apply to" is set to "Paragraph," click the "None" option and confirm with OK.