Older adults with subjective cognitive decline (SCD) may be at a greater risk of cognitive impairment than older adults without SCD (i.e., non-SCD). This study examined dual-task changes in cerebral oxygenation and performance to determine whether these changes may be used as a biomarker in older adults with SCD. Older adults with (n = 24) and without SCD (n = 18) completed neuropsychological assessments and finger tapping and working memory dual-tasks. Cognitive and motor performance were measured, and functional near-infrared spectroscopy (fNIRS) was used to measure changes in prefrontal cortex oxygenation (∆HbO2, ∆HbR). Repeated measures ANOVAs revealed greater ∆HbO2 during the n-back dual-task compared to the single motor (p = .01) and cognitive (p = .04) conditions. Slower responses (p = .002) and less accurate (p = .024) and more variable (p = .001) finger tapping were observed during the dual compared to single tasks. Within the SCD group, ∆HbO2 was greater during the dual compared to single cognitive condition (p = .002) and between the SCD and non-SCD groups (p = .016). Within the SCD group, finger tapping was more accurate during the single compared to dual-task (p = .04). Cognitive accuracy was also higher during the single compared to dual-task condition in the SCD (p textless .001) and non-SCD (p = .005) groups. Neural compensation and inefficiency were observed in older adults with SCD: n-back performance was maintained but double number sequence performance declined despite increased ∆HbO2. Longitudinal evidence is needed to determine whether these mechanisms can be used as biomarkers for progressive cognitive impairment in SCD.