Police believe he was killed during a domestic-related incident at St Marys and later dumped on a secluded road at Greengrove.

A motorcyclist discovered the man, believed to be aged in his 40s, in bush near the intersection of Mangrove Creek Road and Wisemans Ferry Road about 7.30am.

Police arrested a man, 35, and a woman, 36,  shortly after the victim's body was found.

Charges have yet to be laid.

"The man's death is currently being treated as suspicious and police are appealing for any information about the circumstances leading to the man's death," a NSW Police spokesman said.

The man's body had yet to be formally identified and police are still trying to contact his next of kin.

He was found a few kilometres from a yoga retreat but staff said police had not come to question them.

Police taped off an area of road and bush where the body was found and the area has been forensically examined.

Detectives from the homicide squad, St Marys, Brisbane Waters and Lake Macquarie have been involved in an investigation and worked together to arrest the pair that remain in custody.

Police will prepare a brief for the coroner.

Anyone with information was urged to contact Crime Stoppers on 1800 333 000.

• Domestic Family Violence Counselling Service 1800 737 732, Men's Referral Service 1300 766 491