You can use javascript like the following to make a link active in RTB WYSIWYG mode just like a button etc.

Note: Please add the sample script to the end of .aspx page containing RichTextBox – like put the script after the </form> tag but before the </body> tag

Be sure to add _x5 to the ID of RichTextBox as this refers to the RichTextBox IFrame element.

<script language=javascript>

          function modifySelected()

          {

            var selectedText = RichTextBox1_x5.document.selection;

            var newRange = selectedText.createRange();

            var obj = newRange.parentElement();

            if (obj.href)

            {

              window.open(obj.href, "NewWindow"); //Opens the link in new window

            }

          }

      RichTextBox1_x5.document.body.onclick = modifySelected;

</script>