Johnson, a 23-year-old midfielder for Hoffenheim, has joint German-U.S. citizenship and represented Germany at the youth and Under-21 level.
Former Germany coach Klinsmann has also called in Frankfurt born full-back Timothy Chandler, who made two appearances under former U.S. coach Bob Bradley.
Chandler, who plays for Nuremberg, will compete with Hannover 96's Steve Cherundolo for the right-back spot.
The U.S. will host Costa Rica in Carson, California on September 2 and then face Belgium in Brussels four days later.
Klinsmann, who began his reign as U.S. coach earlier this month with a 1-1 draw against Mexico, has also given a chance to Colorado Rapids midfielder Jeff Larentowicz, who has just one previous appearance for the Stars and Stripes.
Mexico-based trio Jose Torres, Michael Orozco Fiscal and Edgar Castillo were also named to the squad that features established starters Clint Dempsey and Landon Donovan.
Squad:
Goalkeepers: Bill Hamid (D.C.United), Tim Howard (Everton)
Defenders: Carlos Bocanegra (Glasgow Rangers), Edgar Castillo (Club America), Timmy Chandler (Nuremberg), Steve Cherundolo (Hannover 96), Clarence Goodson (Brondby), Zach Loyd (Dallas), Michael Orozco Fiscal (San Luis), Heath Pearce (Chivas USA), Tim Ream (New York Red Bulls)
Midfielders: Kyle Beckerman (Real Salt Lake), Clint Dempsey (Fulham), Maurice Edu (Glasgow Rangers), Fabian Johnson (Hoffenheim), Sacha Kljestan (Anderlecht), Jeff Larentowicz (Colorado Rapids), Robbie Rogers (Columbus Crew), Brek Shea (Dallas), Jose Torres (Pachuca)
Forwards: Juan Agudelo (New York Red Bulls), Jozy Altidore (AZ Alkmaar), Teal Bunbury (Sporting Kansas City), Landon Donovan (Los Angeles Galaxy).
