As long as lobster is dead before being cooked it is not poisonous in the slightest. It is extremely important that you make sure your lobster is dead before cooking it because the last thing you will want is to ingest bacteria from it. Because of the fact that lobster like most other crustaceans tend to spoil very quickly after they die because of certain digestive enzymes, it will be important to boil yours alive.
If the head of the lobster is cut off soon after it does, the meat will be much fresher when it is cooked. By freezing your lobster you will be able to slow down the processes which can lead to bacterial contamination. Since you will want to avoid food poisoning at all costs, it will be necessary to make sure that your lobster is dead before cooking and eating it.