Subjective measurements of thermal comfort (TC) and temperature sensation (TS) are used to assess thermal environments, but tend to have large inter-individual variability, making them unsuitable for group descriptions of subjective feelings. As a consequence a more objective measure of thermal perception would be useful. Nielsen et al (2001), found a strong relationship between oesophageal temperature (T_oes) and the α/β index of electroencephalographic (EEG) activity during cycling in the heat. When a similar protocol was followed, a relationship between the subjective measurement of rating of perceived exertion (RPE) and T_oes was established (Nybo & Nielsen, 2001). As TC and TS are correlated with both T_oes and RPE (via body temperature), the possibility exists that α/β index reflects TC and TS rather than T_oes. This hypothesis was tested in the present experiment. Following ethical approval and informed consent, the EEG activity of fifteen cortical regions (F₄,F₃,F₇,F₈,C₄,C₃,C_z,P₄,P₃,O₂,O₁,T₄,T₃) were recorded (Trackit T24, Lifelines, UK) in five physically active males during three, 20 minute periods of cycling at work intensities that elicited 50, 75, and 85% of maximum heart rate, followed by 40 minutes of rest. Each trial was conducted in 35^oC air, 50% RH. Fast Fourier transformation was used to obtain power spectrum areas in α (8-13 Hz) and β (13-13 Hz). Percentage change of α and α/β activity from rest were used as indicators of arousal level (Nielsen et al, 2001). TC, TS, RPE and rectal temperature (T_RE) were also measured alongside the EEG recordings. Pearson correlation coefficients were used to describe any relationships. Paired-sample t-tests were used to analyse comparisons. During exercise T_RE increased by 1.02 ± 0.3°C to 38.51± 0.52°C. Increases in TRE and RPE were significantly correlated (r = 0.91; P<0.001). Increases in T_RE were associated with an elevated α activity in the frontal regions F₃ (r = 0.567; P<0.05) and F₇ (r = 0.66; P<0.05). Elevations in α activity and RPE were also correlated in these regions (F₃: r = 0.66; P < 0.05; F₇: r = 0.56; P<0.05). No relationships were established between α and α/β activity and TS or TC. With the omission of RPE, by comparing α and α/β activity during and post-exercise rest, at the same T_RE, α/β activity was only significantly elevated at the cortical region F₄ (9.00 ± 22.37% vs. 33.24 ± 10.66%; P<0.05). However, a 1°C increase in T_RE caused an increase (P<0.05) in α/β activity in all the frontal regions (F₃: 4.31 ± 32.52% vs. 58.99 ± 50.00; F₄: 11.50 ± 12.68% vs. 48.74 ± 17.12; F₇: -7.59 ± 10.87% vs. 55.04 ± 30.16%; F₈: 1.78 ± 17.22% vs. 45.77 ± 24.12%). It is concluded that changes in brain activity are not a valid objective measurement of TC and TS. Therefore, the experimental hypothesis is rejected. Brain activity also appears to be associated with alterations in T_RE rather than RPE.