Golding, the group's leader, and Fransen, his deputy, were found guilty of actions that were hostile toward Muslims, according to the Sky News broadcaster.
The Britain First group was spreading their materials during the rape trial, in which several Muslim men were eventually convicted.
The judge reportedly found that Fransen and Golding, arrested in May last year, had been trying to use the rape case to promote their political goals.
Deputy Leader of far-right Britain First Jayda Fransen, who was retweeted vigorously by the President of the US, has been found guilty of a hate crime (religiously-aggravated harassment)— Humza Yousaf (@HumzaYousaf) March 7, 2018
Perhaps President @realDonaldTrump will now wish to disassociate himself from Britain First? pic.twitter.com/wYSVLdnfJU
The Britain First describes itself as a movement committed to the national sovereignty and independence. The group says that it is firmly against racism, and invited UK nationals of all backgrounds to join its activities.