The office said that Apple's arguments in support of the patent "are not persuasive." The office didn't invalidate the patent, but it ordered Apple to submit more evidence to support it.
Even if the patent office invalidates the patent, it remains valid through the long appeals process that could reach the US Supreme Court.
The San Jose federal courtroom is a 15-minute drive from Apple Inc.'s Cupertino headquarters, and several prospective jurors were dismissed because of their ties to the company.
Lawyers for South Korean-based Samsung Electronics Co. complained to the judge Tuesday that when Apple attorney Harold McIhenny told the jury that US television makers were driven out of business for failing to protect their intellectual property, it was an unfair attempt to inflame jurors' prejudices.
Judge Koh denied Samsung's demand for a mistrial, but she did call jurors back from deliberations to reread an instruction ordering them to put aside their dislikes and biases in deciding the case.
The two companies are locked in legal battles around the globe for supremacy in the more than $300 billion smartphone market.
