The neurocognitive mechanisms associated with mindfulness training in children are not well understood. This randomised controlled study with active and passive control groups examined the impact of an 18-week mindfulness curriculum delivered by schoolteachers on emotion processing in Vietnamese 7- to 11-year-olds. Event-related potential markers indexed emotion processing while children were completing emotional Go/No-Go tasks before and after mindfulness training, and at 6-month follow-up. In an oddball Go/No-Go task with Caucasian faces no changes in P3b and LPP components were detected, but in a Go/No-Go task with Caucasian and Japanese faces changes were observed in P3b latencies and LPP mean amplitudes. Specifically, the P3b in response to angry non-targets for Japanese faces peaked later in the mindfulness training group (TG) at 6-months follow-up in comparison to the non-intervention control group (NCG). The LPP mean amplitudes for averaged Caucasian and Japanese angry non-targets were also attenuated in the TG at 6-month follow-up. In contrast, no changes in the LPP mean amplitudes were observed for the NCG over time. Together, these findings may indicate that mindfulness training in pre-adolescents enhances emotional non-reactivity to negative distractors. A fluctuating pattern of LPP mean amplitude modulations for angry targets was observed in the active control group (ACG) receiving social-emotional learning (SEL) training. Overall, findings from this study suggest that mindfulness training in pre-adolescents enhances emotional non-reactivity to negative distractors and some of the effects are culturally sensitive.