The Nikkei index started the week down 22.02 points at 10,820.78 on the Tokyo Stock Exchange, after closing at its highest level in nine-and-a-half months on Friday.
The Middle East unrest and rising Portuguese debt yields may weigh on equity sentiment Monday, especially as the Nikkei looks technically overbought, said Tsuyoshi Segawa, equity strategist at Mizuho Securities.
"The index continues to look top-heavy," he told Dow Jones Newswires.
Fears have grown that hundreds of people were killed in a brutal government crackdown on demonstrators demanding an end to Moamer Kadhafi's 41-year, iron-fisted rule.
As the protests crept nearer the Libyan capital Tripoli, the turbulence shaking the Arab world following the revolutions in Egypt and Tunisia also spread to Morocco, where thousands rallied for change across the country.
But Segawa said a large sell off was nevertheless unlikely, with investment funds continuing to flow into global equity markets on the back of credit-easing measures and due to strong US and Japanese economic fundamentals.
US stocks closed higher Friday for the third straight weekly gain, hitting fresh two-year highs in a late-session rally ahead of a long holiday weekend.
The Dow Jones Industrial Average gained 73.11 points (0.59 percent) to finish at 12,391.25.
That was the blue-chip indicator's highest level since June 2008 and left the Dow with an 11th week of gains in the past 12 weeks.
US equity and bond markets will be closed Monday in observance of the Presidents Day holiday.
The dollar fetched 83.16 yen in early Tokyo trade Monday, unchanged from New York late Friday. The euro rose to $1.3700 from $1.3691.