The trade group's Pending Home Sales Index slipped slightly, dropping 0.6 percent in the month to 102.1 after the the group revised September reading slightly higher to to 102.7.
The index is 1.6 percent lower than the October 2012 reading of 103.8.
The index has moved steadily away from May's six-year peak when the housing market was frequently cited as a solid contributor to the economic recovery.
NAR Chief Economist Lawrence Yun in a statement said the government shutdown in October derailed some deals.
The partial government shutdown "sidelined some potential buyers," he said. "In a survey, 17 percent of Realtors reported delays in October, mostly from waiting for IRS income verification for mortgage approval," Yun said.
He also said the downward trend may level out soon.
"We could rebound a bit from this level," Yun said.
"Job creation and a slight dialing down from current stringent mortgage underwriting standards going into 2014 can help offset the headwind factors."
The NAR said the Pending Home Sales Index for the Northeast rose 2.8 percent to 86.8. The index in the Midwest rose 1.2 percent to 104.1.
Those gains were offset by declines in other regions, NAR said. In the West, the index dropped 4.1 percent to 93.3 while in the South it fell 0.8 percent to 114.5.