If you mean perform magick, yes! Magick is simply the directing of will in a way that causes change - you can do that without having any idea what you're doing.
A spell is a magickal operation that involves things like incantations and candles. If you're doing all that and you don't know about it then you're probably having one of those crazy Ambien-induced sleep-activities. I gotta say, sleep-spells would kick the pants right off of sleep-eating!
Our emotions and energies are past around often, especially when we are in crowds of people. That is why many that are 'spiritually conscious' (if you will) can feel depressed or angry (or any negative emotion) after coming out of a large public place, like a mall; it is simply easy to pick up on that energy, a lot of it can be negative.
In some regions of africa, misfortunes are sometimes blamed on people who for some reason transform their negative emotions into malevolent magic. They are often unaware of their magic, and are detected by "witch smellers" Personally I think this is nonsense and transference, but it is an example.