Police in Menlo Park said they were alerted to the threat by authorities in New York.
A bomb squad is said to be on the scene and a building was evacuated.
Authorities have asked people to avoid the 200 block of Jefferson Drive while they investigate.
A police spokesman said: "Avoid the area of the 200 block of Jefferson Drive in Menlo Park. Police are investigating a bomb threat.
"The building at 200 Jefferson was evacuated and San Mateo County allied agencies bomb units are on scene going through the building."
It is understood both Facebook and Instagram have offices at the site.
More to follow…
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