What do you do when you find someone staring at you?

okay, so i always find people staring at me and i have no clue what to do, i usually just look away and pretend i dont notice, but five minutes later theyll still be looking. even if i make a small annoyed look they still look. i mean do ALL of them just randomly space out and look at me?? i mean im a girl and i also find a lot of girls looking, like when im walking in the hallways, theyll just look at me until i p by or if im in the library, whenever i come in with my friends, i always see them look up, i mean i wud get if u looked for like a second to see who it is, but they just continue, it happens with guys too, but more with girls! what does that mean?? im straight, just saying, so itl help with the answer!! thanxxxxx :D