The investigation was triggered after a viral e-mail was sent out to publicise The Decoy, a novel by Tony Strong, a senior copywriter at AMV.
Sources say a placement team at the agency had been briefed by Strong to create a concept to publicise the book, which contains scenes of necrophilia.
The resulting viral, sent from AMV's server, was a graphic film showing a man having sex with a corpse.
Michael Baulk, the AMV chairman, said: "It came to the management's attention on 18 July that an e-mail had been sent out by the AMV server the day before, related to a private project by an employee. That e-mail was in very clear breach of the company policy. Its contents were immediately condemned ... and an apology issued to all recipients."
The agency's management is investigating why the AMV server was used.
Baulk added that it had not yet been decided if the issue will result in disciplinary action.
Strong has been out of the agency since the event and did not return calls.