WordNet sense 1 (a strong feeling of anxiety):

trouble

WordNet sense 2 (something or someone that causes anxiety; a source of unhappiness):

concern, headache, vexation

WordNet sense 3 (be on the mind of):

interest, occupy

WordNet sense 4 (be concerned with):

care

WordNet sense 5 (disturb the peace of mind of; afflict with mental agitation or distress):

vex