Police said the accident happened at just before 13:00 at the event in Blaxhall, north-east of Ipswich.
The air ambulance service attended and the man was pronounced dead at the scene, a police spokeswoman said.
She said there were "not believed to be any suspicious circumstances" surrounding the incident and a file would be prepared for the coroner.
Club secretary Lyn Berwick from Woodbridge DMCC, which is based at the Blaxhall track, confirmed it was not one of their riders who had died, but said the man had been competing at the purpose-built circuit.
At the time it was hosting the penultimate round of Eastern Centre Championship, with riders from across East Anglia.
She said members of the club were with the deceased's family but declined to comment any further.
A man in his 20s has died after falling from his bike at a motocross event in Suffolk.