I had surgery a month ago and have been fine, but the last two days I've had a low grade fever. Should I be concerned? I had cervical fusion surgery on my neck a month ago and have been fine, but the last two days, I've had a low grade fever of around 99.

No. It is very unlikely that your low grade fever represents an infection in your neck. If your symptoms persist, it would be wise to see your primary care dr. For evaluation.
Need to be checked. Infection is not a common problem with neck fusion but it does occur. Time course is not that unusual for a post-operative infection - needs evaluation of you by the surgeon and possible imaging, blood work, examination,
Your . Your low grade fever may be secondary to a separate issue such as a viral illness, urinary tract infection, or other infection. Do you have any other symptoms? If so this points to another issue and should be addressed by your primary care provider. Do you have pain or swelling in your neck? If so contact the doctor that performed your surgery. He/she may want to see you for a follow up. Take care.