One activist braved rain and laid down on the highway leading north from the capital, an activist from the "You Stink" movement told AFP, adding that she was then detained.
The AFP journalist saw dozens of activists on a highway southeast of Beirut, standing in the middle of the thoroughfare to block traffic for several minutes before being pushed back by security forces.
"Today we are sending a message to the government, these were symbolic actions," said activist Assad Thebian.
"We are in discussion with unions and organisations to step up our action for next time."
While traffic on two of the three highways where activists had gathered was flowing normally again by mid-morning, protesters stayed put on the Dawra highway, north of Beirut, Thebian said.
Rubbish has piled up on beaches, in mountain forests and river beds across Lebanon since the closure in July of the country's largest landfill at Naameh, just south of Beirut.
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On Saturday, the government said it would temporarily reopen a landfill, but "You Stink" and other civil society movements that oppose the plan pledged to block roads and called for a general strike.
The activists' demands include a transfer of waste management to municipalities and a boosting of the country's rubbish recycling capabilities.
Some 3,000 protesters marched to central Beirut on Saturday, demanding a permanent solution to the crisis, with some carrying banners calling for the "fall of the government".
In past demonstrations, protesters have repeatedly rejected the reopening of the Naameh landfill, calling for a comprehensive and long-term solution to the crisis.
Naameh was set up in the early 1990s as a temporary measure.
Earlier this month "You Stink" posted on its Facebook page a jarring video of mountains of trash festering across Lebanon.
In one of the shots filmed by a drone, plastic bags containing rubbish can be seen stretching for miles like a flowing river.
The footage, which was widely shared ahead of the demonstration, mocked the tourism ministry over a video it had commissioned to highlight Lebanon's natural beauty.