The 24-year-old admitted to investigators that he was the biological father of the baby and also told officers that he has been "in a relationship" with the pregnant girl since October.
The age of consent in Oklahoma is 16.
The 12-year-olds mother was also arrested on suspicion of child neglect and enabling child sex abuse.
In an unrelated case, the girls father is in prison serving a 12-year sentence for a rape conviction.
Photo: Getty