You're probably reading a bit too much into your child's behavior — 3- to 6-month-old babies are learning to focus on objects, to pick particular things out of everything they're seeing. Some objects or toys may be more interesting to your baby than others, but she may not actually be bored at all.
If she's alone with her toys, maybe she just doesn't enjoy the solitude. As she gets older and learns how to entertain herself, she'll become much more content to play on her own. In the meantime, remember that you're not responsible for keeping her busy and amused every moment of the day.
Edward Christophersen, clinical psychologist. (No Date). Why does my baby seem restless and bored with her toys?. Baby Center [Online]. Available: http://www.babycenter.com/404_why-does-my-baby-seem-restless-and-bored-with-her-toys_6872.bc