A member of the public contacted police after making the find in an area off the A198 at about 6.30pm on Sunday, close to the 19th century home.
Detective Superintendent Pat Campbell said: "We are in the very early stages of this investigation, to recover the remains, identify the deceased and inform their family, and establish the circumstances of the death.
"The recovery will be a painstaking process and officers and scientific experts will be in the area doing this work over the coming days.
Built by the 7th Earl of Wemyss between 1790 and 1800, it was one of the last great architectural commissions of the celebrated architect Robert Adam.
More recently, it starred in time-travel TV series Outlander, where it doubles for the stable block at the Palace of Versailles..