There was a time when putting a comma between a last name and an abbreviation like Jr. and Sr. was mandatory. But that’s no longer the standard, except on the Yahoo! front page where it sometimes appears in names:
Since 1993 The Chicago Manual of Style recommends that no comma be used in names like Martin Luther King Jr. It also notes that if you use the comma before Jr. or Sr., the comma sets off these abbreviations, so an additional comma is needed after the abbreviation.