An uninhabited island off the coast of Arnhem Land may seem worlds apart from medieval Africa, but believe it or not, they're more connected than you'd think.

In 1944, a RAAF serviceman found several coins on a deserted beach on one of the Wessel Islands, off the Northern Territory coast, but the exact location of the discovery remained a mystery.

Now, almost eight decades later, amateur historians believe they've found another coin — this time on Elcho Island, which is also in the Wessel Island group.

The 1944 coins were linked to the east African city of Kilwa, off modern-day Tanzania.

If confirmed to be the same Kilwa coin — thought to have been produced post-1400 — the new coin would be among the oldest foreign artefacts ever found in Australia.

"One of our archaeologists, he found a coin on the surface of the beach on Elcho Island … and it's the same size [as the Kilwa coins]," amateur historian Mike Owens said.

Past Masters archaeologist Mike Hermes discovered the copper coin on a recent field trip to Elcho Island. ( Supplied: The Past Masters )

"There are a number of very well-known watering sites around the island … so these things would have been known for centuries."

Though little is known about how a piece of medieval Africa found its way onto a remote coastline off the Arafura Sea, it offers a glimpse into a bygone time.

The copper coin has now been sent to Canberra, where further testing will be able to confirm whether or not it holds a hidden history.

"It'll take at least weeks, but if the copper content is the same … then that'll be it really," Mr Owens said.

"It is very frail and very thin, but it's the right size, the right weight, the right colour and our experts think this coin is from east Africa because there's nothing else comparable.

"If it does turn out to be a coin it will be an extraordinary event and it will generate an incredible amount of work and expeditions.

"These things can be life-changing and a find like this, it will be by far the oldest ever imported thing in Australia."

'X marks the spot' for 1944 discovery

For Mike Owens and the Past Masters — a group of amateur historians, archaeologists and researchers exploring Australia's place in more than 1,000 years of trade — the discovery has been a long time coming.

Since 2013, Mr Owens and his colleagues have been combing the Wessel Islands coast trying to unravel the mystery of the Kilwa coins.

First uncovered in 1944 by RAAF serviceman Morry Isenberg on one of the archipelago's beaches, little is known about the discovery site itself.

"We were trying to locate where they [the original coins] were found," Mr Owens said.

"[A colleague] had marked the map, so we had a treasure map … there was an X marking the spot, [but] it turned out to be the wrong spot.

Mike Owens believes the discovery could be confirmed as a Kilwa coin. ( Supplied: The Past Masters )

"So over the last five years we've been trying to discover the blasted thing."

The Past Masters hope that if they find the same site traversed by Mr Isenberg, they will find more coins.

That will allow historians to piece together timeframes and possibilities as to how they got there in the first place.

"If you had the coins on board a ship at Kilwa … and headed into the rising sun … if you kept doing that, you would hit the Wessel Islands," Mr Owens said.

"So it's possible a German freighter took them to the old possessions in Papua New Guinea.

"Or they were washed down the dunny of a 747."