The epicenter of the quake, which struck at 2215 GMT, was located 24 kilometers (15 miles) west-southwest of the town of Champerico, and 180 kilometers west-southwest of Guatemala City, the US Geological Survey said.
The Pacific Tsunami Warning Center said there was "no destructive widespread tsunami threat" based on the data.
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On Wednesday, a 7.4-magnitude quake struck in the same area, killing 42 people, according to an updated death toll given by President Otto Perez. Initially, 52 people had been reported dead.
Last week's quake was the most violent to strike the central American country since 1976, when almost 23,000 people perished.
