The activists, whose number added up to several dozens, came from such groups as the US Campaign for Palestinian Rights and Jewish Voice for Peace.
They called for the US government to divert funds to domestic priorities such as affordable housing and childcare instead of further arming Israel with American weapons.
One activist was arrested after he climbed up onto a 51-foot (15.5 m) high black steel sculpture, unfurling a large banner and waving the Palestinian flag.
Other protesters chanted "ceasefire now" and wore shirts with the slogan "invest in life" as they linked arms.
US Capitol police said they arrested 51 people in total as a result of the demonstration.
Reuters images show activists engaging in civil disobedience in Hart Senate Office Building, which is part of the US Capitol complex where many senators and committees have their offices.
"Funding more death and destruction of human life...makes no one secure, and instead fuels hatred and continued war," said Sandra Tamari, the executive director of the Adalah Justice Project, one of the groups involved in the protest.
"The Senate must heed our urgent demand to stop funding militarism and instead invest in life," she added.
The Gaza health ministry said on Monday that Israel's genocide in the blockaded territory, which started on October 7, has so far killed over 18,200 people and wounded 49,645 others
RHM/Press TV