During memory consolidation, extracellular signal-regulated kinases (ERK) regulate the expression of several proteins involved in synaptic plasticity, but they also show other important roles locally at the synapse. There are many studies that explore ERK synaptic activation, most of them focusing on Long Term Potentiation at a specific moment in time. Here, our aim is to describe time-dependent ERK activation in the synaptosomes of mice hippocampus after a learning experience. Using an Inhibitory Avoidance task, we trained different groups of mice: Unshock (Un), Shock (Sh), and Immediate Shock (ShI). We measured ERK activation levels in the cytosolic compartment 45 minutes after training, and in the synaptic content -the soluble protein fraction within the synaptosomes- at 5, 15 and 45 minutes after training. We found that, in the cytosolic fraction, there is a dramatic decrease in phosphorylation levels in most experimental groups compared to naïve animals. In particular, ERK2 showed the greater differences, as it is commonly observed. At the synaptic compartment, however, the differences appeared only in ERK1 in ShI vs Sh, and ShI vs Un at 15 and 45 minutes respectively, but not 5 minutes after training. Thus, our results show that synaptic activation of ERK differs greatly from the general cytosolic activation, suggesting differential kinetics and potential functions.