Colin Speirs, whose age was given as 'unknown', was a member of a band which attended events in Broughshane and Ballymena in April and May in 2021.
At Ballymena Magistrates' Court the defendant, of Inchcolm Avenue in the town, admitted two charges.
A prosecutor said on May 14, 2021, an estimated 150-200 people took part in an unnotified public procession in Broughshane "in relation to the Irish Sea Border".
She said there were visual warning signs warning about taking part in the unnotified procession "and also the offence of breaching the current health regulations which were in place at the time".
The prosecutor said a "verbal warning" was also given by police at the gathering and "those warnings didn't deter or change the defendant's actions".
She said police footage showed the defendant was a drummer in a band and he was "recognised through his distinctive facial and arm tattoos".
The court heard the second charge related to April 24 in 2021 when an estimated 400 people gathered in the Wakehurst Road area of Ballymena "despite the current coronavirus regulations at that stage".
The prosecutor said the regulations meant outdoor gatherings were limited to no more than 10 people from two households.
The prosecutor said there four bands and numbers in attendance then grew and "approached 1,000".
The court heard the defendant was pictured on police footage as a band drummer and "again noticeable by his distinctive facial tattoos".
She said the defendant walked past a visual warning and was also in the area whenever police issued verbal warnings.
The prosecutor said neither procession had been notified to the Parades Commission and said she believed "at least another two people" are being prosecuted.
A defence lawyer said the the defendant had "nothing to do with" the organisation of the parades but was a member of a band "invited to participate".
The solicitor said he had made enquiries and the Public Prosecution Service said his client was the only person brought to court in relation to one of the events.
District Judge Nigel Broderick said although it did not give the defendant "a defence" he would like more information from prosecutors to see "how equitable" the prosecution was.
The prosecutor said she had spoken to a colleague who said there were large numbers of people at the parades and "were police submitted admissible evidence sufficient to identify a person taking part, whether that is organisers, marshals, bandsmen or simply a walker in the parade, then those persons were considered under the prosecution test".
The prosecutor said her colleague said he would need to "undertake research" to see if anyone prosecuted was an "organiser or a marshal".
The defendant was given 100 hours Community Service.