So you've already created the object? Then it's as simple as using as the is
operator.
var obj = Activator.CreateInstance(...);
bool objIsIMyInterface = obj is IMyInterface;
If you'd like to test at the point you've created a System.Type
, you can use Type.IsAssignableFrom
:
Type type = ...
bool typeIsIMyInterface = typeof(IMyInterface).IsAssignableFrom(type);