Training accuracy decreases
The screenshot looks like output of Keras, so I assume you're using a deep neural network. The training (epoch) is organized with batches of data, so that optimization function is calculated within subset of whole dataset. The console output shows the accuracy of the full dataset, so the optimization of a single batch can decrease the accuracy of the other part of the dataset and decrease the global result.

The other possible reason is that you provide test set to Keras API and the console output is result of the test set that is not used for training of the model. If it's true you can see that your model is overfitting.