The detention took place on Friday, 7 October in Faro, and involved a 42-year-old woman who was on a red alert from Interpol.
In a statement, SEF did not specify the nationality of the detainee, pointing out that she is "a foreign citizen" who will be extradited.
Interpol's red alert called for the suspect's arrest.
According to SEF, the alert was issued on September 27 and "provided the fulfilment of a six-year prison sentence as the reason for the arrest".