Yes, it is quite normal, but you would better avoid watching tv for a long time, or you may have some vision problems. Because the eyes have muscles which can control the movement of the eyes, so if you keep your eye muscles stand in a spot for a long time and not move a muscle, you will soon become fatigued and will lose your focus, so pay attention to that.
According to what you said, it is normal for you to feel your eyes are out of focus after watching TV a whole afternoon. When you watch TV, you are likely to tilt your head gradually or you may have the habit of supporting your head with your arm while watching TV, so you may find yourself casting a sidelong glance. Moreover, a whole afternoon! What a long time it is! You must have strained your eyes so that they are out focus now. You should have a good rest and do not overuse your eyes now. Apply warm compresses over your eyes can make you feel better. Remember not to spend too much time on TV or computer in the future. After a certain time of using the eyes, you should rest them and do some eye exercises to avoid eye strain.