Best way I can expalin it is that Im just extremely interested in what ever it is Im staring at.
I do that myself, I just stare at things for long periods for no apparent reason, but for me I am always thinking of something different to what I am staring at, I just call it my phase out time. I dont think its nothing to worry about, sometimes Your brain takes time out also, but just as a precaution do go and see your GP and get his professional advice, maybe its your brain telling you that you need some time out alone to think.
I don't think it is anything to worry about. Does it interfere with what you are doing? Some folks, myself included, will just sort of stare into space for a few seconds, my mother used to call them "staring spells" it is nothing, maybe just the brain taking a few seconds off, but, really, I don't think it is serious.
Are these things you stare at inappropriate things? Is the staring accompanied by disturbing or odd thoughts? Do you have any troubling flashbacks or memory lapses when you do this? If not it's probably nothing to be concerned about. It may be a light case of ADHD attention deficit type or something, especially if the starring distracts you from important things that require focus like school work. Let me know if this helps!