Chile's index dipped for the fourth consecutive session while Brazilian stocks eked out a small gain, continuing a nine-day winning streak that gave the Bovespa its biggest boost in 11 months.
The Fed, whose $85 billion bond buying program has supported investor appetite for risky emerging market assets, is due to release minutes from its July meeting on Wednesday, and investors will be seeking clues on the timing of possible stimulus tapering.
Mexico's IPC stock index shed 1.34 percent on Monday in its third down session to close at 41,484.25 points, notching its biggest dip since July 29.
The biggest drag came from a dip in billionaire Carlos Slim's telecom company America Movil,, which saw its shares fall 2.79 percent to 12.92 pesos per share, its lowest close since late June.
The company announced earlier this month an offer for the 70 percent of Dutch telecoms group KPN that it does not already own, defying Spanish rival Telefonica's bid to buy KPN's German unit E-Plus.
Brazil's Bovespa barely managed to continue its winning streak with a 0.07 percent gain to close at 51,574.09. The streak has given the index its biggest boost since September 2012.
Brazil's gains were led by SA Gerdau, which saw shares up 5.78 percent after HSBC Securities analysts raised the recommendation and price target on the steelmaker's preferred shares.
Chile's IPSA index fell 0.74 percent, its fourth consecutive session of losses to close at 3,702.92. The index was pulled down by shares of retailer Cencosud, which lost 3.09 percent.
Data on Monday showed Chile's economic growth marked its slowest rate of expansion in nearly two years in the second quarter as domestic demand grew more slowly.