This is a complex topic, worth developing at length elsewhere. Jonathan Alterman made a great down payment on this in his book “What Liberal Media.” Here’s a brief overview:
It depends on what you mean by “liberal.”
It’s widely accepted that many, probably most journalists at news outlets considered conservative, like Fox News, generally tend to hold right of center views. Many, maybe most mainstream journalists at news outlets considered liberal, like MSNBC, tend to hold left of center views.
They tend to be well-educated urban dwellers. Their opinions tend to be liberal.