Are Halos Biblical?

Halos weren't even invented by Christians. Halos actually came from the religion Zoroastrianism, an old religion that is still practiced today. Halos were invented in the 300bc, Christians adopted halos in the 5th century, using them at first only for angelic beings and God, but later giving it to the saints and Mary. Since it has these origins, I recommend avoiding using it in art, but that is your choice to make.