According to the Zimbabwe Lawyers for Human Rights, detectives raided her house in Harare early on Friday morning and confiscated her laptop and other electronic equipment.
A 25-year-old American journalist charged with attempting to overthrow Zimbabwe's President Robert Mugabe, on account of an alleged tweet that described the ageing leader as "selfish and sick", was remanded in custody Saturday after denying the accusations.
The AP also reports that the Zimbabwe Lawyers for Human Rights say they have represented almost 200 charged for allegedly insulting the Zimbabwe president in recent years. The subversion charges carry up to 20 years in prison.
The tweet had a photo illustration of the 93-year-old Mugabe with a catheter, the charge sheet said. He added that his client had formally been charged with insulting the president.
Ms O'Donovan denied the allegations as "baseless and malicious".
O'Donovan is accused of referring to Mugabe when she tweeted about a "Goblin" whose wife and step-sons imported an expensive auto.
U.S. Citizen Martha O' Donovan, right, appears at the Harare Magistrates court escorted by a plain clothes police officer shielding her face in Harare, Saturday, November, 4, 2017.More news: HTC U11+ Release: What You Need to Know
Recent online reports have claimed Mr Mugabe's two adult sons, Robert Jr and Chatunga, have imported at least one luxury vehicle from neighbouring South Africa.
Martha O'Donovan is charged with subversion and insulting the president for allegedly calling Mr Mugabe a "sick man" in a tweet, according to the Associated Press.
Mugabe last month appointed a minister for cybersecurity, a move criticized by activists as aimed at clamping down on social media users.
Zimbabwe authorities say they believe O'Donovan is the author of the tweet on October 11 based on her IP address.
Zimbabwe was shaken a year ago by the biggest anti-government protests in a decade.
Zimbabwe Lawyers for Human Rights says it has represented almost 200 people charged for allegedly insulting Mugabe, the world's oldest head of state, in recent years.