The woman in her early 20s was spotted by a fellow juror listening to music as she was meant to be helping try the case of a pensioner accused of bludgeoning his wife to death after 50 years of marriage.
She could now be charged with contempt of court and, if convicted, may be punished with an indefinite jail sentence and an unlimited fine.
Details emerged after the defendant was convicted and Judge Roger Chapple lifted a reporting restriction which prevented previous publication of the details for fear of disrupting proceedings.
The woman had repeatedly arrived late for hearings at Blackfriars Crown Court, central London, and prosecuting lawyer Peter Clarke asked for her to be dismissed.
The judge initially refused, saying it was not necessary, but a day later, he received a note from another juror suggesting that the woman may have been listening to music during the defendant’s evidence.
A Metropolitan Police spokesman said that police were called by a judge hearing a case at Blackfriars “regarding the inappropriate actions of a juror.”
“A woman was arrested for contempt of court on the direction of the judge,” he added. “Following the conclusion of the trial, the judge has requested that the matter be investigated.”
Lawyer Benn Maguire, a member of the team prosecuting the murder case, said: “It is unique for all those who are connected with this court to experience a situation where the juror is suspected of listening to a MP3 player under her Islamic headgear.”
He added that he expected the woman would go to prison if she was charged and found guilty of contempt.