To see a box in your dream signifies your instinctual nature and destructive impulses. Alternatively, you may be trying to preserve and protect some aspect of yourself. The box may also symbolise your limitations and restrictions. Consider the pun of “being boxed in”.
To dream that you are opening a box indicates an aspect of yourself that was once hidden is now being revealed. It symbolises self discovery. Consider your feelings as you open the box. If opening the box fills you with fear, then you may be uncovering aspects of yourself that cause you to feel anxious.