Justifications? Well, yes:
You experience a world, right. It seems to be full of other people, like you. They seem to also experience a world, and by comparing experiences and building machines which measure the world, it seems that our experiences of the world are the same. We can also see how other people stop and start existing without the world doing so.
That leaves us three options.
Option 1: There is a physical, objective world beyond the mind. You are like one of the other people, a part of the world. The world is not a part of you. The world didn't start with you and will not end with you.
Option 2: There is a physical, objective world beyond the mind, but it's not the one you are experiencing. You are in fact being induced to hallucinate this world instead of the real one. Probably because aliens somehow want to use your body as an energy source, even though that claim makes so scientific sense and is about the worst plot device ever. Nothing you do can break this illusion, there is no blue or red pill.
Option 3: There is no physical world outside your mind, there is only you. You are alone and god. For some reason, when you started existing, you for no particular reason started hallucinating that you were human being that was a couple of years old. And for some really inexplicable reason, you hallucinate a reality over which you have no control. Although you can make yourself a rock star with infinite amounts of money and sex, you hallucinate yourself sitting in front of a computer asking interesting philosophical questions on a website. Nothing you do seem to be able to break the hallucination that the world you hallucinate is not a hallucination.
Now, option 2 is clearly absurd, and option 3 doesn't make any sense. If the world really was your hallucination, why aren't you hallucinating something better?
So yes, there is justifications for assuming that there is an objective world outside of your mind: Everything you experience tells you there is, and nothing you do can break that experience. The only reasonable assumption in that case is that the world in fact is objective and exists outside and independently of your mind.