Testosterone is naturally found in the females, certainly at much lower levels than it is found in males. In fact, testosterone is the precursor molecule from which which estrogen is produced through the action of an enzyme called aromatase.
So as long as the testosterone level falls within normal range of a healthy female, this is perfectly normal. If however the testosterone level is increased, further investigations may be required. The most common causes are usually related to ovarian cysts (polycystic ovary syndrome).