Is it ok if you are 14 years old and 5 feet 3.25 inches and weigh 84 pounds or are you underweight?

Possibly, but it is unlikely. A person with a BMI that low (18 to 25 is considered to be in the "healthy" range) can be at risk of health problems. A doctor should be consulted. They will be able to accurately say if there is a health problem or underlying condition that may be causing this, or if you are perfctly healthy.