A juror has been charged with illegally playing detective during a criminal trial.

A 47-year-old man appeared briefly in the Melbourne Magistrates Court on Tuesday accused of conducting research when a juror in a County Court trial on or about December 6, 2012, into a matter relevant to the trial without the authorisation of the trial judge.

No details of the trial were revealed in court and police refused to comment but academic Jacqueline Horan, in her book Juries in the 21st Century, claimed a juror in Victoria had caused a mistrial in December 2012 after he allegedly looked up the definition of "beyond reasonable doubt" on the internet.

The maximum penalty for the charge, under the Juries Act 2000, is a fine of 120 penalty units (more than $17,000).

The court was told the man would be pleading not guilty to the charge.

No case conference had been held as yet but there had been preliminary discussions between the parties.

Deputy Chief Magistrate Jelena Popovic adjourned the case for a contest mention on a date to be fixed.

Juries Commissioner Paul Dore told Fairfax Media it was not the first time a juror had been charged in Victoria with playing detective.

Under the Juries Act, a juror "must not make an enquiry for the purpose of obtaining information about a party to the trial or any matter relevant to the trial, except in the proper exercise of his or her functions as a juror".

The act says "making an enquiry" includes consulting another person or conducting any research by any means such as using the internet to search an electronic database for information.

A juror is banned from viewing or inspecting a place or object that is relevant to the trial; conducting an experiment; and requesting another person to make an enquiry.

Both Supreme and County Court judges routinely warn jurors not to research the case against an accused person before a trial begins.

Latest Victorian Law Reform Commission figures reveal there were 579 Supreme and County Court jury trials in 2011-12 with 446 in Melbourne and 133 in regional Victoria. In 2012-13, there were 584 jury trials in Victoria with 448 in Melbourne and 136 in regional Victoria.

Supreme Court Justice Phillip Priest was last year forced to discharge a jury in the trial of Steve Constantinou, charged with murdering stripper and sex worker Johanna "Jazzy O" Martin, after a juror fell asleep while he was telling them how they must not base their verdict on any information obtained outside the courtroom.

"You must not make any investigations or inquiries or conduct any independent research concerning any aspect of this case or persons connected with it," Justice Priest told the jury. "This includes any research about the law that applies to the case.

"You must not use research tools such as the internet to access legal databases, earlier decisions of this or other courts or other matter of any kind relating to matters in the trial.

"You mustn't search for information about the case on Google or conduct similar searches.

"You are jurors, you are not investigators, and you must not take into account material that has not been properly presented to you as evidence.

"It is also important you base your decision solely on the information provided in court or otherwise under my supervision.

"You must understand that Parliament has made it a criminal offence for jurors to make any inquiries for the purpose of obtaining information about the people in the trial or the matters relevant to the case."

A second jury found Constantinou guilty and he was later jailed for 24 years.