The highway was closed since shortly after 4 p.m. Saturday as police collected evidence in the area well into Sunday morning, Sgt. Doug Calcagno said.
The Paratransit driver was identified by San Leandro police as Eddie Hall, 31, of Oakland.
CHP Sgt. Trent Cross said it appears the crash followed an altercation between the driver and the motorcyclist, who he said was a Hells Angels member.
The motorcyclist had been traveling in a group with seven or eight other motorcyclists, Calcagno said.
The Paratransit van struck the motorcyclist, and the motorcycle was dragged under the van for several miles before the van pulled over just east of the 150th Avenue onramp, Calcagno said.
After Hall pulled over to the shoulder, he attempted to flee the scene and was arrested by Alameda County Sheriff's deputies, San Leandro police said.
Calcagno said that there were no passengers in the Paratransit van at the time.
The motorcyclist was treated by Alameda County Fire Department personnel and then transported to a nearby hospital. He was pronounced dead shortly after arriving at the hospital.
San Leandro police and CHP are investigating whether Hall intentionally struck the motorcyclist.
"We don't think it was an accident," Calcagno said, but said it was unclear what the motive may have been.