The stock market's consistent push higher has made traders and investors a lot of money, but now it is making some of them uneasy.
The market's strong run hasn't missed a beat in the new year, as equities continue to climb at a brisk pace. The S&P 500 is up roughly 3% so far this month and has climbed more than 9% just since the beginning of November.
JC O'Hara of MKM Partners, citing an old adage about rapidly rising markets not correcting by moving sideways, said in a note to clients to "swim at your own risk" at these elevated prices. A pullback could be around the corner.
"I think it is safe to say this market has risen further, faster than most think," O'Hara said.
Tony Dwyer of Canaccord Genuity is also taking a cautious stance after the recent run, moving his market view to neutral from positive. The technology sector in particular appears to be overbought in a way that has historically preceded a drop of more than 13%, Dwyer said in a note to clients.
"History has shown that either a long-duration consolidation period or a nasty pullback can help relieve market excesses, and we have evidence the move higher in Tech has created the type of environment that generated temporary corrections in the pre-dotcom era," Dwyer said.
The lack of volatility in the market has also made Wall Street wary. The S&P 500 hasn't had a daily move of more than 1% in either direction since October, O'Hara said, creating an abnormally calm market. The realized 30-day volatility for the index is near 100-year lows, Michael Wilson of Morgan Stanley said in a note to clients.
Risk is skewed toward volatility rising, Wilson said, but a catalyst may be needed to create that move. Once the extended period of calm breaks, the markets could be rattled, O'Hara said.
Several technical indicators show that the market may be near a peak. For example, the Cboe Put-Call Ratio for equities, which measures option activity, is at its lowest level in more than five years, according to Bank of America's Stephen Suttmeier. When the ratio is low, it may be a sign that investors are too complacent and the market is overbought.
To be sure, some, such as Credit Suisse's Jonathan Golub, are still bullish on the market as some economic indicators show signs of a turnaround. Golub raised his year-end target on the S&P 500 to 3,600 from 3,425, projecting an 8% gain from where the index currently trades.
"The prospects of better economics and earnings are fueling the most recent leg higher, and the data suggests that this trend will continue," Golub said in a note to clients.
Still, there are signs that the broader investor community isn't sold that the bull market will continue. Bernstein said in a note to clients that the first two weeks of the year saw the highest level of inflows into bond funds in the 15 years it has tracked that data.
Those investors, like many strategists and traders, are skeptical of putting more money into stocks at these heights.
"Since early December, we've been bullish on the S&P 500 but the higher the price goes, the higher the risk of a negative surprise," Wilson said.
— CNBC's Michael Bloom contributed to this story.