Brahma is traditionally said to have originally had five heads before one was removed, leaving the familiar four-headed form.
Hindu stories give more than one explanation for the missing head. In one account, Brahma became infatuated with a goddess identified variously as Saraswati, Savitri or Gayatri. As she moved around him, he produced additional heads so he could continue watching her, including a fifth head above him. In another important legend, Brahma’s fifth head spoke arrogantly against Shiva and asserted Brahma’s superiority. Shiva, or his fierce form Bhairava, severed it.
Brahma is therefore commonly represented with four faces, often interpreted as looking toward the four directions. The four heads are also associated in later iconographic explanations with the four Vedas. The missing fifth head is a mythological detail rather than a claim about a historical image or a uniform doctrine across every Hindu text.
This question can cause confusion because several Hindu deities have five-faced forms, known as panchamukha. Five-faced Hanuman, Shiva and Ganesha are separate iconographic traditions. For Brahma’s origin-and-removal story, however, the expected answer is five.