Pretty sure.
Would you allow Mage Armor and Bracers of Armor to stack? They both offer an armor bonus. Think of Mage Armor as a tangible force that takes the place that Armor would take up. Thus, you can't wear armor over or under it. HOWEVER, you *Can* cast it, and benefit from it when incorperal creatures try to get you, since your regular armor bonus from armor doesn't stack (except magical bonuses).
Page 104 PHB, top right hand collum.
Would you allow Mage Armor and Bracers of Armor to stack? They both offer an armor bonus. Think of Mage Armor as a tangible force that takes the place that Armor would take up. Thus, you can't wear armor over or under it. HOWEVER, you *Can* cast it, and benefit from it when incorperal creatures try to get you, since your regular armor bonus from armor doesn't stack (except magical bonuses).
Page 104 PHB, top right hand collum.
Bonuses from armor and a shield stack. This bonus is an armor bonus, so it does not stack with other effects that increase your armor bonus, such as mage armor spell or braers of armor.