We report a positive exchange bias in thin film multilayers produced with nano-oxide layer. The positive exchange bias resulted from an antiferromagnetic interfacial exchange coupling between the ferromagnetic CoFe and the antiferromagnetic CoO layers, which spontaneously forms on top of the nano-oxide layer during the subsequent deposition of a CoFe layer. The shift in the hysteresis loop along the direction of the cooling field and the change in the sign of exchange bias are evidence of antiferromagnetic interfacial exchange coupling. The high temperature positive exchange bias observed for our system results from magnetic proximity effects between CoFe and CoO.