Sounds like contamination. What steps do you follow to ensure template-free and template-only workflow? Once you have a contamination event with a synthetic DNA a lot of precautions and decontamination are necessary. Decontaminate hard\non-porous surface. Throw away reagents and work with small aliquots always; I prefer the one and done approach for aliquots.

• I agree with Jeffrey. That sounds like contamination: make fresh aliquots of 10uM primers from parent stock. Use a fresh aliquot of 0.2u filter sterilised molecular grade water and use this both to dilute primers and dilute your PCR mix. In addition try amplifying from a fresh aliquot of your amplicon 

Hi Shukkoor,  in addition try to use filter tips for all steps and must replace your entire pipette set dedicated for qPCR work with a new set as may be they are badly contaminated internally mainly from the cDNA concentrate you have, thus contributing this uniform pattern of signals of contamination in successive sets of runs. Either this issue exists in the reagents and water source as mentioned by the respected colleagues above or in your pipettes or even both. The signal of dust also and often gives a positive band from NTC +ve amplification wells on the gel. So invigilate your working environment too. You can correlate the melt curve peaks' temperature of your reaction wells and NTC with each other to reach some conclusion, as usually if there is no contamination in your NTC so if any peak is there its mainly the primer dimers, such PD peaks are low in height, a bit broad (not as sharp as product) and at low Tms than the product peak or to the peak due to some major contamination in your setup. Also use a proper range well-resolved ladder on gel to exactly differentiate your product  size (which is known to you) with other nonspecific bands which could also be near to your product size and the bands of primer dimers. 

Thanks Every one, I will do the experiments and will update ..