Mila Kunis -- Alleged Stalker Strikes Again

A homeless man tailed Mila Kunis to a gym Friday -- a man who law enforcement says is a stalker -- and he was detained after Kunis' security sounded the alarm.

Law enforcement tells TMZ, the man is being investigated by authorities but there was not sufficient evidence to arrest him so he was freed -- but he could be arrested once the investigation is completed.

We do not know how many prior incidents Kunis has had with this individual, but we're told there is a history.