Is it possible for numbers to say you're underweight, when you're really an ok weight?

This is an odd question so I'll explain :) My BMI says I'm slightly underweight. However, I don't exercise much and muscle weighs more than fat. Also, I don't really have curves (boyish figures run in the family, sadly) so maybe a lack of boobage contributes to me having a low weight? Even bones could weigh different amounts, right? Anyway, I was wondering whether it's possible that, due to what I've mentioned, I'm actually a healthy size despite not weighing much, ie BMI doesn't account for bone mass, muscle mass, or breast tissue/lack thereof :p Also, my parents think I'm a healthy weight. Do you think it's possible my BMI is an inaccurate guideline?