Yes but you'll have to go through the hierarchy yourself:
var instance = new B();
Type t = instance.GetType();
bool isA = false;
while(t != typeof(object))
{
if(t.IsGenericType && t.GetGenericTypeDefinition() == typeof(A<>))
{
isA = true;
break;
}
else
{
t = t.BaseType;
}
}