250 is too large for a primer dimer and the band is clear and sharp. You have an unexpected amplification from another sequence or pseudogene or member of a gene family. If you cannot ignore it to get the result that you want then you could either design new primers or run a DMSO gradient of 1% to 8%dmso and hopefully at some concentration the unwanted amplimer will disappear if the primers do not have exact homology with the template dna

The size of the primer is too large, I think it is better to re-design it.

Dear Aakash,

It's improbable that the 250 bp band is due to primer-dimer. Given that the primer-dimers are usually generated because of complementarity between the used primers notably at the 3' end, the size of the product cannot be more than the sum of the size of both primers together (typically 20-50 bp). In addition, primer-dimers look generally like a smear or diffused-looking band on the gel, the 250 bp band in your gel looks like a sharp clean band. Consequently, I think that this band is a result of unspecific amplification.

Here is a list of tools that can be useful for you:

https://molbiol-tools.ca/PCR.htm

Some of these tools allow you to verify the specificity of the used primers and even check for potential primer-dimer formation.

Finally, if you want to make sure of the amplified product, the best solution would be to sequence each band separately by using a gel extraction/purification method.

Good luck,

YS