Body Mass Index (BMI) is a measure of your weight in relation to your height; it is not a measurement of percent body fat.
BMI is used to indicate if you are underweight, at a healthy weight, overweight or obese. If you are overweight or obese, just losing 10% of your body weight can improve your health.
BMI has some limitations in that it can overestimate body fat in persons who are very muscular and it is only one of several ways to assess your weight and health risk. If you have any concerns regarding your body weight, always discuss them with your doctor.