Far infrared radiation drying (FIRD) of Ecklonia cava was tried in order to reduce drying time and save money in an industrial processing of wet seaweeds. FIRD was carried out at temperature range of 40-$80^{circ}C$ with the examination of antioxidant activities as compared to freeze drying (FD). FIRD showed the shorter drying times and higher polyphenolic contents than FD. Most FIRD extracts had $IC_{50}$ values than FD extracts. Among them, absolute methanolic extract (ME) from E. cava dried by FIRD at $40^{circ}C$ (FIRD40-ME) possessed the highest radical scavenging activity. Moreover, FIRD40-ME enhanced cell viability and $H_2O_2$ scavenging activity in Vero cell. Thus, FIRD40-ME was separated by high performance liquid chromatography (HPLC) and radical scavenging activities of the separated compounds were directly evaluated by on-line coupled $ABTS{cdot}+$ radical scavenging detection system. From the result, it was found that dieckol was the major antioxidant compound. These results illustrate that antioxidant activity of FIRD were more effective than FD and industrial application of FIRD process can be useful in seaweeds.