Praise be to Allaah.
It is forbidden for men to pluck their eyebrows.(al-Mawsoo’ah al-Fiqhiyyah, part 14, Tanammus)
It is not permissible for men, just as it is not permissible for women, to trim their eyebrows. Islam forbids plucking even one hair, and trimming could affect every hair, which is worse. (This was the fatwa of our shaykh, Shaykh ‘Abd al-‘Azeez ibn Baaz, when he was asked this question verbally).
But if the eyebrows are causing harm, such as falling over the eyes and preventing one from seeing properly, they may be trimmed as much as needed to remove the problem. (From a discussion of the matter with Shaykh ‘Abd-‘Allaah ibn Qa’ood).
And Allaah knows best.