A court in the northern city of Haifa ordered Yevgeny Grossman, 22, held in police custody until another hearing on 10 March.
Grossman denied allegations he helped primary suspect Eliran Golan target Arabs, including Arab-Israeli legislators.
Israeli police earlier arrested Golan who confessed to a three-year bombing campaign against Arabs and to plotting the assassination of Israeli Arab lawmakers.
Police said Eliran Golan, 22, had begun his attacks soon after the start of the Palestinian uprising in the West Bank and Gaza, but the only casualty of the 10 homemade bombs he planted was a woman injured in an explosion at a mosque.
"It turns out that the infrastructure of Jewish terrorism...is still alive and kicking"
Golan was arrested at his family's home in the northern city of Haifa, where police found an explosives laboratory and more than 30 bombs ready to use. Police said Golan had confessed and they now wanted to find out if he had acted alone.
"He was in the middle of planning an attack," said Northern District police chief Yaacov Borovsky. "He was planning to target lawmakers and Arab-Jewish couples and places where Arabs and Jews met together."
Golan's father had also been detained but had denied any involvement, police said.
On Golan's hit-list were the most prominent members of parliament from the Arab 20% of Israel's population. He had already placed a bomb under the car of one Arab deputy in the Knesset, Issam Makhoul.
"I think they only uncovered the tip of the iceberg," said Makhoul. "It turns out that the infrastructure of Jewish terrorism...is still alive and kicking."