Gillian Sturgeon, aged 46, was arrested on Wednesday in connection with an incident that occurred within a property in Kilwinning on Saturday, August 7.
Her arrest came days after a 50-year-old man was also arrested over the same incident.
The precise circumstances of what happened are not yet known.
Gillian Sturgeon, a mother-of-two, is the First Minister’s younger sister.
She posted on social media: “I know that the police have a duty to investigate and I have fully co-operated.
“I can make no further comment at this stage but I am confident that the truth will prevail.”
Gillian Sturgeon, sister of First Minister Nicola Sturgeon, arrested over incide…
Both Ms Sturgeon, who lives in Irvine, and the man have been released and are scheduled to appear at Kilmarnock Sheriff Court at a later date, police have said.