Yes. It may harm your eyes by its UV rays, continuous light from the monitor, and a strained accommodation of your eye muscles, apart from other factors.
You may have backache or shoulder ache from bad sitting posture. Repetitive stress injuries may affect your fingers, wrists etc due to excessive/improper mouse/keyboard use.
There may even be maladjustment of your circadian rhythm, that may cause irritability and insomnia.
So, it is recommended that you go through the safety guidelines, to be safe and secure.