Westbrook was notably left out when starters were announced last week.
The 26-year-old Cousins, averaging a career-high 28 points per game, will be an All-Star for the third straight season in his seventh season in the NBA.
First-time All-Stars DeAndre Jordan of the LA Clippers and Gordon Hayward of the Utah Jazz highlighted the rest of the seven West reserves as announced Thursday on TNT. Golden State Warriors stars Klay Thompson and Draymond Green, and Memphis Grizzlies center Marc Gasol were also tabbed as All-Stars in the West.
The seven reserves from the East are: