U.S. Attorney Joseph Russoniello said that Jeffrey Schinkel, 34, of Novato, was arrested this morning.
Russoniello said Schinkel pleaded not guilty at an arraignment before U.S. Magistrate Edward Chen in San Francisco and was ordered held in custody for the time being.
Schinkel's next court appearance is scheduled before Chen on Tuesday for identification of his defense lawyer.
Russoniello said a federal criminal complaint filed against Schinkel alleges that he communicated with an undercover Immigration and Customs Enforcement agent about child pornography, invited the agent to join a members-only child pornography Web site, and then viewed the Web site.
Schinkel is charged with knowingly having access to a Web site that contains child pornography with intent to view child pornography.
The crime carries a possible maximum sentence of 10 years in prison but the actual penalty, if Schinkel is convicted, would be determined after consideration of federal sentencing guidelines.
Christine Gasparac, a spokesman for California Attorney General Jerry Brown, confirmed that Schinkel was an investigator for Brown's office, which is known as the state Department of Justice, but declined to give details about his job.
She said the department was informed of the federal investigation of Schinkel in June and cooperated with the probe.
Gasparac said, "After today's arrest, Agent Schinkel's peace officer powers will be suspended, his credentials and all issued equipment confiscated, and he will be the subject of an internal investigation."