鼓励 is almost always positive. Common patterns: 鼓励某人做某事 (encourage someone to do something), 受到鼓励 (receive encouragement), 互相鼓励 (encourage each other).
usage
Compare with 激励 (jīlì, to motivate/inspire — stronger), 鼓舞 (gǔwǔ, to inspire/uplift — more about morale), and 表扬 (biǎoyáng, to praise — more about commending).