For men were injured in the attack, the party said, and a police case has been filed.
Leader of the opposition and former Chief Minister Jagadish Shettar said the attacks on BJP workers have been continuing in Karnataka.
"More than 26 activists have already died. Yesterday also, there was a murderous attack on BJP workers," Mr Shettar said. Alleging that there was a "Goonda raj" in Karnataka, he said he was warning the state government. "Every day, we are discussing in the assembly about a failure of law and order and Congress goondaism," he said.
The BJP - which is hoping to wrest power from the Congress in Karnataka -- has pitched law and order as one of the key issues in the coming assembly elections in the state. It has been flagged repeatedly in election rallies by its star campaigners, including Prime Minister Narendra Modi, who spoke of the "ease of doing murder" in the state earlier this month.
Karnataka home minister Ramalinga Reddy has questioned the validity of the BJP claims, saying the police will be asked to investigate whether the attack on the BJP workers was carried out by the Congress or it was a BJP claim for "publicity and the forthcoming elections".
Mr Shah, the minister said, had contradicted himself, claiming at one point that the man targetted at the restaurant, Vidvat, was a BJP activist. "After some time he (Amit Shah) said, 'just for political reasons I told like that. He is not at all our party worker'. We can't believe these BJP statements," he added.
"What about Haris's son? What about Narayanaswamy who wanted to burn an entire government office? Is goondaism by Haris's son created by BJP?" asked Mr Shettar.