Popocatépetl from the ISS on January 23, 2001
It might be (and is likely) just normal behavior for Popocatépetl in Mexico, but the volcano produced six plumes over the last 24 hours, according to a report out of Mexico City (in spanish). Officials from El Centro Nacional de Prevención de Desastres (The National Center for the Prevention of Disasters - Cenapred) say that the plumes appear to be mostly water vapor and other volcanic gases, but remind people living near the volcano to be vigilant.
Popocatépetl is only 70 km from Mexico City, so any major eruption from the volcano could affect life and air travel to the major metropolis. The last major eruptive period at Popocatépetl ran from 1996-2003, producing VEI 3 eruptions, but the volcano has been producing smaller eruptions since January 2005. The volcano produces a mixed bag of activity, with ash fall, lava flows, pyroclastic flows and lahar generation and might be one of the more hazardous volcanoes in the Americas.