This Bible contradiction is from the Skeptic's Annotated Bible.

Verses

Aaron died on mount Hor.

Numbers 20:27-28 View context

And Moses did as the LORD commanded: and they went up into mount Hor in the sight of all the congregation.

And Moses stripped Aaron of his garments, and put them upon Eleazar his son; and Aaron died there in the top of the mount: and Moses and Eleazar came down from the mount.

Numbers 33:38 View context

And Aaron the priest went up into mount Hor at the commandment of the LORD, and died there, in the fortieth year after the children of Israel were come out of the land of Egypt, in the first [day] of the fifth month.

Aaron died at Mosera.

Deuteronomy 10:6 View context

And the children of Israel took their journey from Beeroth of the children of Jaakan to Mosera: there Aaron died, and there he was buried; and Eleazar his son ministered in the priest's office in his stead.