Peaking at 10 p.m. EDT, the flare was accompanied by another solar phenomenon known as coronal mass ejection that can send solar material out into space.
This CME was not Earth-directed, the space agency said Monday.
Solar flares are powerful bursts of radiation, and while harmful radiation from a flare cannot pass through Earth's atmosphere to physically affect humans on the ground, if intense enough they can disturb the atmosphere in the layer where GPS and communications signals travel, causing radio blackouts.
The blackout associated with this flare has since subsided, NASA said.
"X-class" flares are given a number based on their strength; X2 is twice as intense as an X1, an X3 is three times as intense, and so forth.
NASA has classified Sunday's flare as an X1.7.
Increased numbers of flares are expected because the sun's normal 11-year activity cycle is ramping up toward solar maximum, which is expected this year, the space agency said.