Look at the sidewall of the tire if it is marked front or rear the tire is designed with a specific position in mind. It may also include rotational direction arrows. Without any marking I assume it is a multidirectional and multiposition tire.
Most of BMXers I know put wide tire in front and narrower one for the rear (2.35 vs 2.10, sometimes rear have slicker protector). However some use the same for front and rear, I remember Cory Martinez has same. I myself have Animal Tom White 2.0 in rear and Animal GLH 2.35 in front.