Yes Venom has a post credit scene, two of them actually but the first one is a doozy. Stop reading if you don't want a spoiler
The following spoiler is from the good folks at MovieWeb
Eddie Brock (Tom Hardy) will still be a journalist by the end of the film. Now pursuing new leads for a story, Brock travels to the famous San Quentin prison to interview a dangerous murderer. The killer in question is none other than Cletus Kasady, the man who becomes the infamous supervillain Carnage.
Kasady, who's played by Woody Harrelson in a red-haired wig, asks Brock if he "wants to hear the carnage," referring to his murders. Obviously, name-dropping his alter ego makes it clear who this character is intended to be, for those unfamiliar with the Cletus Kasady name. During their conversation, a piece of the Venom symbiote can be seen lurking its way towards the serial killer, before the scene cuts to black. Clearly, what's being set up is a confrontation between Venom and Carnage in a sequel, and we're already being given an explanation as to how Carnage comes to be in this universe. With there still being uncertainty as to whether we'll ever see Spidey show up in a Venom sequel, Carnage seems like the obvious go-to for Eddie Brock's next foe.