The last time 2014-JO25 was in our immediate neighborhood was 400 years ago, and it's next brush with Earth won't happen until sometime after 2600.
The April 19 flyby is an "outstanding opportunity" for astronomers and amateur stargazers, NASA said.
"Astronomers plan to observe it with telescopes around the world to learn as much about it as possible," the US space agency noted.
Besides its size and trajectory, scientists also know that its surface is twice as reflective as that of the Moon. It should be visible with a small optical telescope for one or two nights before moving out of range.
2014-J25 was discovered in May 2014 by astronomers at the Catalina Sky Survey near Tucson, Arizona.
Also on April 19, a comet known as PanSTARRS will make its closest approach to Earth at a "very safe" distance of 175 million km (109 million miles), according to NASA.
The comet has brightened recently and should be visible in the dawn sky with binoculars or a small telescope.
Asteroids are composed of rocky and metallic material, whereas comets — generally smaller — are more typically made of ice, dust, and rocky stuff.