My friend has just got into the University of Amsterdam's neuroscience masters course, even though her undergrad was in a different subject (biochemistry) - so it certainly is possible, at least with some courses. I'm also about to start a masters in a subject that is pretty different to my undergrad - it's more common than you think!
I'd advise that you check the course requirements for different courses you're interested in and see which accept people with different backgrounds - contact the unis directly if it's not clear and ask. Also, anything you can do at this stage to demonstrate your interest in the new subject won't hurt your application - for example, attending open lectures or writing a few relevant articles for your uni newspaper.
Good luck!