(Read more: Goldman: Stay out of emerging markets)
The firm likes several relatively pricey sectors. One is U.S. technology stocks, based on strong corporate free cash flows and prospects for corporate earnings growth. The Dow Jones U.S. Technology Index has gained about 141 percent over the past five years.
Another is high-yield credit, based on relatively low leverage and yields relative to investment-grade bonds. The Vanguard High-Yield Corporate Fund is up nearly 35 percent over the same period.
A separate Goldman division issued a strong warning Monday about a likely market correction. The trading firm's strategists called the S&P 500 valuation "lofty by almost any measure" and attached a 67 percent probability to the chance that the market would fall by 10 percent or more—the technical yardstick for a correction.
(Read more: 'Lofty' market ripe for at least 10% drop: Goldman Sachs)
Mossavar-Rahmani was clear that U.S. stocks were more expensive after a roughly 30 percent gain for 2013.
But she reiterated the four reasons Goldman believes equities are not in bubble territory, as outlined in a recent strategy report: Credit growth is not excessive; investors are just beginning to get back into U.S. stocks; views on the U.S. are not yet overly bullish; and stock valuations have not raced too far ahead.
In other words, there's too much risk and cost involved in taking money out of the stock market now.
"This is not a blind endorsement of buy and hold," Brett Nelson, a managing director in the investing strategy group, said at the same briefing. "You need to consider a broader mosaic of factors to make an underweight decision and not simply rely on valuation as a stand-alone factor."
(Read more: As bulls run, Deutsche Bank isn't so sure)