No, you are not. Otherwise, the alternator’s windings will burn because the mains is not working synchronously with the generating set.

If you want to connect your house to a generating set, you can use a transfer switch (3-position switch) or an automatic start/stop system. That way, either the mains or the generating set serves as a source of energy for your house.
 
If you want to make the mains and the generating set work together, you can make use of a parallel circuit. By using a parallel circuit, you make sure that the output voltage and the frequency of the generating set and the mains are synchronous and that there is no phase shift between the generating set and the mains.