The space rock had been invisible to astronomers until January 5, but scientists quickly calculated the asteroid, named 2018 AJ, will fly past Earth Tuesday, January 23.
But NASA admits it is not yet certain of its orbital path.
New asteroids are given a condition code of between 0 to 9 based on how certain astronomers are about its course.
Zero means they are fairly certain, but 9 is classed as “highly uncertain”.
It is currently believed it will pass at a comfortable 4.6 times the distance from Earth to the Moon.
The Moon is 238,000 miles from Earth and this pass, currently estimated at around 1.1 million miles, is considered a cat’s whisker in astronomical terms.
NASA considers and monitors anything which comes within six million miles of our planet as a near earth asteroid.
The asteroid is estimated to be between 22 and 68 metres in diameter, meaning it is bigger than a three-storey house.
If something of that size did impact Earth, it could decimate a whole city.
In February 2013, an unknown 19-metre meteor came from nowhere to explode in the sky above Chelyabinsk, Russia, with the force of 500,000 tonnes of TNT.
And the energy released shattered glass on hundreds of buildings and more than 1,000 people were injured as a result.
There are millions of asteroids in the solar system, usually found in the Asteroid belt between Mars and Jupiter, however those that pass the Earth are called near-earth objects.
They are small, rocky bodies that orbit the sun, and are often called minor planets or planetoids because they are smaller then planets and even the moon
There were several asteroids discovered last year by NASA, which is continually locating them, but estimates we only know the location of around 3 per cent of those out there.
A NASA spokesman said: “As of December 24, there are 17,495 known Near-Earth Objects (NEOs) around our planet; 17,389 are asteroids.
“Last year, we discovered 1,985 new near Earth asteroids. There were 1888 such objects discovered in 2016 and 1,571 in 2015.”
2018 AJ is from the Apollo group of asteroids, a group of near Earth asteroids that regularly cross the planet.
They were discovered by German astronomer Karl Reinmuth in the 1930s and named after the first one to be discovered, the 1.5km diameter 1862 Apollo asteroid.
The new one, 2018 AJ was first observed by operators of the Mount Lemmon Survey Observatory, in the Santa Catalina Mountains, northeast of Tucson, Arizona.
NASA says it knows of no significant asteroid that is expected to hit the Earth for at least 100 years.
As of January 7, there are 1,872 potentially dangerous objects discovered in the vicinity of the Earth, but none are on a collision course.
Since the beginning of this year, nine more such objects have been discovered.