Persons with aphasia (PWA) have been found in many previous studies to exhibit impaired performance on attention processing tasks, even when these tasks do not contain linguistic stimuli. There is also some evidence that as individuals, PWA may show more intra-individual variability (i.e. time-based fluctuations) in attention than healthy controls. The current study systematically examines two types of intra-individual variability in attention in aphasia, between-session intra-individual variability (BS-IIV) and within-session intra-individual variability (WS-IIV), looking in particular at how task demands impact these dimensions of performance. We administered five novel attention tasks with varying processing demands, three non-linguistic and two linguistic, to 20 PWA and 20 similar-aged healthy controls. Results showed that PWA exhibited higher levels of WS-IIV than controls but that levels of BS-IIV were similar between the two groups. Increased task demands were found to result in increased BS-IIV and WS-IIV for both groups, and there was some evidence suggesting that the addition of language demands may further increase both WS-IIV and BS-IIV in the PWA group. In addition to these group differences, substantial inter-individual variability in WS-IIV and BS-IIV was observed within the PWA group. These findings have implications for better understanding attentional fluctuations in aphasia, as well as how it relates to language deficits in this population, and potentially for better understanding language treatment outcomes.