Only if the creature is hidden solely by invisibility
Being hidden simply means that other creatures are not aware of the hidden creature's current location. This doesn't always rely purely on sight, though that is most often the method used.
Stealth. Make a Dexterity (Stealth) check when you attempt to conceal yourself from enemies, slink past guards, slip away without being noticed, or sneak up on someone without being seen or heard. (PHB, p. 177)
If Johnny is in clear view, and is sneaking up quietly from outside Billy's field-of-view, the Stealth check made is not to see if Billy spots them; that is already not possible as they are not looking in Johnny's direction. Stealth in this situation is to see if they can move quietly, without alerting Billy to their presence. If at any time Johnny were to enter Billy's field-of-view, the Stealth roll would not matter and Johnny would no longer be hidden.
Similarly, if Billy is under the effects of see invisibility, this would not change the scenario, as Johnny's Stealth relies on defeating Billy's ability to hear him approach.
If Johnny is invisible, even if Billy turns around (possibly from Johnny failing his Stealth check to move quietly), Johnny is still not visible. Billy may be able to hear him, and make an attempt to attack, but Johnny would be an unseen target due to the invisibility.
There are particular class features that do produce caveats to this, but given the general scope of your question they aren't appropriate to bring up at this time.