Stiff neck causes

Sitting at the computer desk browsing or typing for a long time causes stiff neck .Long hours of driving the car or sitting and writing for long hours causes stiff neck. Muscles when they are in the same posture for a longer time becomes tired. There is reduced blood flow. You feel the stiffness .Stretch your neck a few times. Tilt your head to the sides a few times. Rotate your head clockwise and anticlockwise. Do this five to ten times. You will feel relief. Sleeping postures can also cause stiffness. Use a pillow to support the neck. Serious and continuous stiffness can be due to spinal problems.

Hey Pushti,
Stiff neck can be because of wrong sleeping posture, long time in one position like peoples doing long time desk jobs, Lack of stretching in a day, Vertebral dysfunction, etc. So depending on your causes the treatment also matters.