Final answer:
The sentence is in active voice.
Step-by-step explanation:
The sentence 'Oprah Winfrey, a philanthropist with her own media empire, has been called one of the most influential women in the world' is in active voice. In active voice, the subject of the sentence performs the action. In this case, Oprah Winfrey is the subject and she is being called one of the most influential women in the world.
Learn more about active voice