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.
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.