Quick Answer is No.
Focus group are intended to be generative, spontaneous and inclusive in nature.
If participants know the subject in advance, they may formulate ideas or study to become more knowledgeable about the subject than the typical audience member. For similar reasons, they also shouldn’t be told who the sponsor is.
You should exclude people who know one another or have expertise in the subject of the sessions. Potential participants can be told what the subject is in general (e.g., “a health topic”), but shouldn’t be told what the specific subject is.
You would also want to exclude questioning “professional” respondents (i.e., those who have participated in focus groups or individual interviews before) who may lead or monopolize the discussion. Typically, the recruitment screeners exclude people who have participated in qualitative research in the past six months.