I would say it's both.  You can just be nervous by nature or your surroundings could make you nervous.  I know I get anxious when I have a big project at work coming due.  You just have to work it out.

I know some people that never had any anxiety issues when they were younger, but once they grow up, get jobs, get lives, etc. Poof its there. Is this something you are really born with or is it all enviromental?