Is onus a negative word?

I'm curious to know if the word "onus" carries a negative connotation. When I hear it, it seems to imply a sense of responsibility or burden that may not always be viewed positively. However, I'm not entirely sure if this is an accurate interpretation. Could you clarify whether "onus" is indeed a negative word, or if it simply denotes a sense of duty or obligation without any inherent negativity?