Previous research has shown that long-term mindfulness training has beneficial effects on cognitive functioning and emotional regulation, but results are mixed regarding single mindfulness exercises, especially on attention and memory tasks. Thus, the present study aimed to analyse the effects of the Focused Breathing Exercise (FB) on cognitive performance, using standardised tests. Forty-six healthy undergraduate students were randomly assigned either to a FB or a Control condition. Two cognitive tasks (the Concentrated Attention task of the Toulouse-Pierron Factorial Battery and the Logical Memory Subtest I from the Wechsler Memory Scale III), along with mood evaluations (the Positive and Negative Affect Scale), were implemented both before and after the interventions. Results showed no significant differences for the attention task and mood evaluations. Nonetheless, the FB enhanced performance for the memory task significantly more than the Control exercise. The findings highlight that mindfulness does not affect equally all types of cognitive performances. Task characteristics may be important and their analysis can help to disentangle how mindfulness interferes with cognitive processes.