not necessarily. once a topic has been locked that topic is no longer up for discussion because it either goes against one of the rules of the site or because people were getting too heated and starting to target each other. if you want to start a thread about a locked topic then your best option is to pm a moderator and administrator who can tell you more specifically why they locked the thread and if it is ok for you to start a new topic from something in the locked thread.

In general if the topic is not locked its open for discussion and people can start new threads about something that is contained in that thread that they want to go off topic for.