The plants are due to be shut down by the end of the year under legislation introduced by the government of former Chancellor Angela Merkel following the meltdown at the Fukushima nuclear plant in Japan in 2011.
But debate is intense in Germany about whether to keep them running longer given a possible energy crisis this winter following a decline in Russian gas deliveries.
The plants, operated by E.ON, RWE and EnBW, account for around 6% of the country's electricity.
Citing unnamed officials, The Wall Street Journal reported that the government had decided to keep the plants running beyond the end of this year. The paper said the decision had yet to be formally adopted by the cabinet of German Chancellor Olaf Scholz, with some details still under discussion.
"The government has not yet made any decision about how to deal with the three remaining German nuclear power plants after the end of this year," a spokesperson told Reuters. "This will happen first in the wake of the results of the stress tests."
An economy ministry spokesperson said the report in the Wall Street Journal "lacks any factual basis".
(Reporting by Andreas Rinke and Markus Wacket; Additional Reporting by Christopher Steitz; Writing by Sarah Marsh; Editing by Edmund Blair and Barbara Lewis)