A reporter said six men and two women were seen being taken away by security forces from the offices of telecom company MTC Touch at Beirut port on Tuesday.
The offices were raided on the orders of Lebanon's attorney-general Said Mirza, according to a statement from the internal security force.
On 20 September, four men who sold mobile phone lines that were only used around the time of al-Hariri's assassination on 14 February were arrested.
The men were on a list of 10 mobile subscription salesmen handed over to Mirza by the UN commission of inquiry into al-Hariri's killing in a massive Beirut bomb blast.
Mirza issued arrest warrants against the four on charges of withholding information about a crime, a judicial source said.
Al-Hariri's killing sparked popular outrage in Lebanon amid a widespread belief that Syrian intelligence agents were involved despite denials from Damascus.
Lebanese authorities earlier this month arrested four former security chiefs in connection with the killing after recommendations from the UN inquiry.