Oman's index falls from Tuesday's 22-month high as bluechip National Bank of Oman (NBO) drops after reaching its ex-dividend date.
Shares in NBO are down 6.7 percent. The company's shareholders approved a cash dividend of 17.5 percent at its annual meeting on Tuesday, according to a bourse statement.
Profit-taking in other stocks also weighs. Bank Dhofar declines 3.9 percent and Raysut Cement dips 3 percent.
The index falls 1.2 percent to 6,101 points, trimming 2013 gains to 5.9 percent.
Elsewhere, UAE markets are mixed in thin trading as investors await fresh cues, which may come in the form of first-quarter earnings.
Dubai's measure slips 0.3 percent to 1,860 points, while Abu Dhabi's benchmark ticks up 0.1 percent to 3,019 points.
Kuwait's bourse climbs 0.3 percent to 6,795 points and Qatar edges up 0.07 percent to 8,579 points.
Qatar Meat and Livestock (Widam Food) gains 4.8 percent after the company posted a profit of OMR75m (US$20.60m) for 2012, up from OMR58m in the previous year. The board proposed a dividend of 40 percent, a bourse statement said.