The Mexican Military is the name given to the combined military forces of Mexico. So far, only ships and personal of the Mexican Navy have been seen onscreen.
Fear the Walking Dead
In the episode Blood in the Streets, both Victor and Luis state that they have a contact who can help them get past the border and into Mexico. In the episode "Sicut Cervus" it is revealed that their contact is a member of the Mexican Navy, who is part of a small flotilla patrolling the coastal waters around Strand's intended destination in Rosarito, Baja California. They open fire on the Abigail after the gunfight between Luis and his contact.
From the conversation Strand and Luis had with their contact, it appears that the main aim of the flotilla that greeted the Abigail appears to be to keep infected ships from making landfall on Mexico's coast. It can be implied that the army is engaged in stopping the infected crossing over the border from the United States, since George Geary, mentions that Mexico had sealed its borders with the U.S. This may account for the lack of soldiers present after Strand and the others got onto land.
However, since there are known (small scale) outbreaks in Baja, it can be surmised that those members of the Mexican Military not involved in defending the border are engaged in similar operations to the U.S. Military in that they are trying to secure safe zones in the larger Mexican cities. It may also be possible that the country at large is overrun, explaining the lack of a large-scale military presence.
So far, only light costal craft of the navy have been seen on screen. However, they appear to be heavily armed as they were able to fire on the Abigail from a distance and do damage. The two officers who were the contacts for Luis and Strand carried side-arms, as they were able to engage in a brief firefight with Victor Strand and Luis.