From the New Scofield Reference Bible: 

 Author Unknown 
 Date of writing unknown 
 Alothough the book does not name it's author Ezekiel 14:14,21 and James 5:11 refer to Job as an historical person. That he may have lived in the patriarchal period is inferred from his great age,various geographical references, and the absence of mention of the law or Tabernacal.