If the text is the Ipsum Lorum place holder text found in Apple iBook Templates, its probably been "squeezed" off a previous page in which you inserted an image or possibly your text on previous page.
The templates usually have linked text boxes already in the book template, an inserted text box will sit of top of the template linked text causing it to flow around the box. If you do not intend using the book template pages and have chosen "default" which looks empty... even if there is no Ipsum Lorum place holder text, its usual to have the linked text box ( empty) on the page. Placing text in that box will automatically generate a new page if text overflows or the overflow of text will pop out at the first usable space on any page.
It could be a combination of these, although I dont undertsand why you cannot delete it as the inserted text box can be dragged around the page or made smaller, Allowing access to the unwanted text!
It may help other to assist if you state which template you are using and what the text is and if you have inserted images which is not in a mask.